Matgnetic core including Fe-based glassy alloy

Abstract

 A magnetic core includes a magnetic core body composed of an Fe-based soft magnetic glassy alloy having a temperature difference ΔT_x of a supercooled liquid of 20°C or more, ΔT_x being expressed by the equation, ΔT_x = T_x - T_g (where T_x is the crystallization temperature and T_g is the glass transition temperature) and a resistivity of 1.5 µΩm or more. The Fe-based soft magnetic glassy alloy contains at least one metallic element selected from the group consisting of aluminum, gallium, indium, and tin, and at least one metalloid element selected from the group consisting of phosphorus, carbon, boron, germanium, and silicon. The magnetic core body is fabricated by toroidally winding a thin ribbon of the Fe-based soft magnetic glassy alloy or by laminating thin ribbons of the Fe-based soft magnetic glassy alloy, or the magnetic core body is a bulk magnetic core body.

Description

[0001] The present invention relates to a magnetic core including an Fe-based soft magnetic glassy alloy which is used for transformers, choke coils, magnetic sensors, and the like.

[0002] As the materials of magnetic cores for transformers, choke coils, magnetic sensors, and the like, 50% Ni-Fe permalloy, 80% Ni-Fe permalloy, and silicon steel have conventionally been used.

[0003] Magnetic cores composed of the above-mentioned magnetic materials, however, have high core loss particularly in a high-frequency band, and at a band of several tens kHz or more, there is a difficulty in use because the temperature of the magnetic core significantly increases.

[0004] Therefore, recently, a magnetic core body in which a Co-based amorphous alloy thin ribbon having low core loss in a high-frequency band and a high squareness ratio, or an Fe-based amorphous alloy thin ribbon having high saturation magnetic flux density and high maximum permeability is toroidally wound, or a laminated magnetic core provided with a magnetic core body in which the same is press-cut and laminated has been used for transformers, choke coils, magnetic sensors, and the like.

[0005] When the thin ribbon described above having a thickness of, for example, 20 µm, is wound or laminated, a space of approximately 3 µm occurs between adjacent thin ribbons because of unevenness of the surface of the thin ribbon. The volume occupied by a thin ribbon in a magnetic core body is referred to as a lamination factor, and the lamination factor in this case is calculated as follows:

The volume of the space occupied in the magnetic core is large, and thus the size of the magnetic core cannot be reduced.

[0006] The present invention arose in an attempt to solve the problems described above, and it is an object of the present invention to provide magnetic cores which have low core loss and which can be miniaturized.

[0007] In order to achieve the object described above, the present invention uses the following structure.

[0008] A magnetic core in accordance with the present invention is provided with a magnetic core body composed of an Fe-based soft magnetic glassy alloy which has: a temperature difference ΔT_x of a supercooled liquid of 20°C or more, ΔT_x being expressed by the equation, ΔT_x = T_x - T_g (where T_x is the crystallization temperature and T_g is the glass transition temperature); a resistivity of 1.5 µΩm or more; and a metallic element other than Fe and a metalloid element, in which the metallic element includes at least one member selected from the group consisting of aluminum, gallium, indium, and tin, and the metalloid element includes at least one member selected from the group consisting of phosphorus, carbon, boron, germanium, and silicon.

[0009] The magnetic core may be provided with a magnetic core body in which the thin ribbon of the Fe-based soft magnetic glassy alloy described above is laminated, toroidally wound, or formed in bulk.

[0010] The magnetic core may be provided with a magnetic core body in which the powder of the Fe-based soft magnetic glassy alloy is sintered in bulk by a plasma sintering process by increasing the temperature at a rate of 40°C/minute or more.

[0011] When a bulk magnetic core is produced by sintering the powder of the Fe-based soft magnetic glassy alloy by the plasma sintering process, preferably, the sintering temperature is set in a temperature range which satisfies the relationship, T ≤ T_x, where T_x is the crystallization temperature and T is the sintering temperature.

[0012] Preferably, a magnetic core in accordance with the present invention is provided with a bulk magnetic core body in which the molten Fe-based soft magnetic glassy alloy described above is cooled and solidified.

[0013] Also, the magnetic core described above in accordance with the present invention, more preferably, has a composition of the Fe-based soft magnetic glassy alloy as follows, in range of atomic percentages:

aluminum	1 - 10
gallium	0.5 - 4
phosphorus	0 - 15
carbon	2 - 7
boron	2 - 10
iron	the balance

[0014] Optionally, the magnetic core described above in accordance with the present invention has a composition of the Fe-based soft magnetic glassy alloy as follows, in range of atomic percentages:

aluminum	1 - 10
gallium	0.5 - 4
phosphorus	0 - 15
carbon	2 - 7
boron	2 - 10
silicon	0 - 15
iron	the balance

[0015] Also, in accordance with the present invention, the Fe-based soft magnetic glassy alloy may contain germanium ranging from 0 to 4 atomic percent, and more preferably, from 0.5 to 4 atomic percent.

[0016] In accordance with the present invention, the Fe-based soft magnetic glassy alloy may contain 7 atomic percent or less of at least one member selected from the group consisting of niobium, molybdenum, hafnium, tantalum, tungsten, and chromium.

[0017] Also, in accordance with the present invention, the Fe-based soft magnetic glassy alloy may contain at least one of the elements nickel and cobalt, at 10 atomic percent or less and 30 atomic percent or less respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 

FIG. 1 is an assembly view showing a laminated magnetic core as an embodiment of the present invention;

FIG. 2 is an assembly view showing a laminated magnetic core as an embodiment of the present invention;

FIG. 3 is an assembly view showing a bulk magnetic core as an embodiment of the present invention;

FIG. 4 is a sectional view showing the main structure of an example of a plasma sintering apparatus used for producing a bulk magnetic core as an embodiment of the present invention;

FIG. 5 is a diagram showing an example of a pulse current form to be applied to the powder material in the plasma sintering apparatus shown in FIG. 4;

FIG. 6 is a diagram showing the dependence of thickness on saturation magnetization, coercive force, and permeability;

FIG. 7 is a diagram showing extracts of data of the thickness dependence shown in FIG. 6;

FIG. 8 is a diagram showing the dependence of thickness on saturation magnetization, coercive force, and permeability with respect to samples having different compositions;

FIG. 9 is a diagram showing the relationship between fracture strain and thickness with respect to samples having different compositions;

FIG. 10 is a diagram showing the dependence of thickness on resistivity with respect to a conventional Fe-based amorphous alloy and a glassy alloy having a composition in accordance with the present invention;

FIG. 11 is a diagram showing the dependence of Fe content on saturation magnetization, coercive force, and permeability;

FIG. 12 is a diagram showing the dependence of thickness on saturation magnetization, coercive force, and permeability, without heat treatment and after heat treatment with respect to an Si-added sample;

FIG. 13 is a diagram showing the dependence of thickness on saturation magnetization, coercive force, and permeability with respect to a conventional Fe-based amorphous alloy and an Si-added glassy alloy in accordance with the present invention;

FIG. 14 is a diagram showing the relationship between thickness and lamination factor with respect to a glassy alloy in accordance with the present invention;

FIG. 15 is a diagram showing relationships between saturation magnetic flux density, coercive force, permeability, and core loss versus thin ribbon thickness with respect to a laminated magnetic core fabricated from a glassy alloy thin ribbon in accordance with the present invention;

FIG. 16 is a diagram showing the relationship between core loss and thin ribbon thickness with respect to a laminated magnetic core fabricated from a glassy alloy thin ribbon in accordance with the present invention;

FIG. 17 shows a DSC curve of alloy powder having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄;

FIG. 18 shows a DSC curve of a sinter obtained from alloy powder having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄;

FIG. 19 is a diagram showing X-ray diffraction patterns of a sinter obtained after alloy powder having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄ was sintered at temperatures from 380°C to 460°C;

FIG. 20 is a diagram showing the dependence of sintering temperature on density, permeability, coercive force, and saturation magnetic flux density with respect to a sinter obtained from alloy powder having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄; and

FIG. 21 is a diagram showing the relationship between magnetic flux density and core loss with respect to a bulk magnetic core produced by sintering alloy powder having a composition of Fe₇₂Al₅Ga₂P₁₁C₆B₄.

[0019] The preferred embodiments of the present invention will be described with reference to the drawings.

[0020] A magnetic core in accordance with the present invention is fabricated, for example, in the shape of a toroid. Hereinafter, a lamination-type magnetic core (laminated magnetic core) will be described. In such a toroidal laminated magnetic core, a magnetic core body is formed by toroidally winding an Fe-based soft magnetic glassy alloy thin ribbon after the Fe-based soft magnetic glassy alloy thin ribbon is fabricated by a liquid quenching process, which will be described below, or a magnetic core body is fabricated by press-cutting an Fe-based soft magnetic glassy alloy thin film to form a ring and laminating the required number of rings. The magnetic metal body is insulation protected by resin-coating, for example, with an epoxy resin, or by encapsulating in a resin case to produce a laminated magnetic core.

[0021] Also, in order to fabricate an EI-shaped laminated magnetic core, after an Fe-based soft magnetic glassy alloy thin ribbon is press-cut so as to be E-shaped or I-shaped to form a plurality of E-shaped and I-shaped thin sections, the E-shaped thin sections and I-shaped thin sections are laminated, respectively, to form an E-shaped core and an I-shaped core, and then, these cores are joined together to form a magnetic core body.

[0022] The required portion of such a magnetic core body is resin-coated, for example, with an epoxy resin, or is insulation protected by encapsulating in a resin case to obtain an EI-shaped laminated magnetic core.

[0023] FIG. 1 shows an example of a toroidal laminated magnetic core. In a laminated magnetic core 1, a magnetic core body 4, in which a thin ribbon 3 composed of an Fe-based soft magnetic glassy alloy, that will be described below, is toroidally wound, is placed in a hollow toroidal resinous case 2 for containing the magnetic core body.

[0024] The case 2 is formed preferably by using a resin such as a polyacetal resin or a polyethylene terephthalate resin.

[0025] Also, an adhesive 5 is applied onto two spots at the bottom 2a of the case 2 for stably fixing the magnetic core body 4 and the case 2. Preferably, the number of spots onto which the adhesive is applied ranges from 2 to 4.

[0026] As the adhesive 5, an epoxy resin, silicone rubber, or the like is used.

[0027] FIG. 2 shows another example of a toroidal laminated magnetic core. In a laminated magnetic core 11, a magnetic core body 13, in which rings press-cut from a thin ribbon 3 composed of an Fe-based soft magnetic glassy alloy, that will be described below, are laminated, is placed in a hollow toroidal resinous bottom case 12 for containing the magnetic core body, and a top cover 14 is fitted into the bottom case 12. Preferably, the bottom case 12 and the top cover 14 are formed by using a resin such as a polyacetal resin or a polyethylene terephthalate resin.

[0028] Among Fe-based alloys, those that are Fe-P-C-system alloys, Fe-P-B-system alloys, and Fe-Ni-Si-system alloys, and the like have been observed to exhibit glass transition. These alloys have however, a significantly small temperature difference ΔT_x in a supercooled liquid region, and thus, cannot substantially constitute glassy alloys.

[0029] On the other hand, the Fe-based soft magnetic glassy alloy in accordance with the present invention has Fe as major constituent, and has a temperature difference ΔT_x of a supercooled liquid of 20°C or more, or of 40 to 60°C or more depending on the composition, which is a significant temperature range, ΔT_x being expressed by the equation, ΔT_x = T_x - T_g (where T_x is the crystallization temperature and T_g is the glass transition temperature). Thus, formation by slow cooling can be performed, enabling formation of relatively thick ribbon-like or linear materials.

[0030] In order to increase the lamination factor, the thickness of an amorphous alloy used for the laminated magnetic cores 1 and 11 is required to be increased.

[0031] Since the conventional amorphous alloys have a significantly small temperature difference ΔT_x in a supercooled liquid region, when a thin ribbon is produced by rapidly cooling a molten alloy having a given composition in the liquid quenching process, the thickness of the ribbon must be set at 50 µm or less in order not to decrease soft magnetism, and improvement in the lamination factor is limited.

[0032] The Fe-based soft magnetic glassy alloy in accordance with the present invention can be formed into a thin ribbon having a thickness of approximately 100 to 200 µm. The magnetic core bodies 4 and 13, obtained by winding or laminating such a thin ribbon, have a high lamination factor, and components can be miniaturized. Also, because of high resistivity, when the thin ribbon having the same thickness is used, core loss can be reduced in comparison with the conventional amorphous alloy.

[0033] In order to obtain an Fe-based soft magnetic glassy alloy having a ΔT_x of 20°C or more, a metallic element other than Fe and a metalloid element are included in the Fe-based soft magnetic glassy alloy.

[0034] The metallic element other than Fe includes at least one member selected from the III-B and IV-B groups, and specifically, preferably, at least one member selected from the group consisting of aluminum, gallium, indium, thallium, tin, and lead, among which aluminum, gallium, indium, or tin is more preferable.

[0035] The metalloid element preferably includes at least one member selected from the group consisting of phosphorus, carbon, boron, germanium and silicon, and, in particular, preferably includes at least one member selected from phosphorus, carbon, and boron.

[0036] Also, by adding silicon, the temperature difference ΔT_x of a supercooled liquid is improved, and thus, the critical thickness for forming the amorphous single-phase structure can be increased. If the silicon content is excessively large, the supercooled liquid region ΔT_x disappears, and thereby, preferably, the silicon content is 15 atomic percent or less.

[0037] Also, the Fe-based soft magnetic glassy alloy may include at least one member selected from the group consisting of niobium, molybdenum, hafnium, tantalum, tungsten, zirconium, and chromium, and, furthermore, may include at least one of the elements nickel and cobalt.

[0038] More specifically, in accordance with the present invention, the Fe-based soft magnetic glassy alloy may be composed of, in atomic percentage, aluminum: 1 to 10, gallium: 0.5 to 4, phosphorus: 0 to 15, carbon: 2 to 7, boron: 2 to 10, and iron: the balance, and incidental impurities may be contained.

[0039] Also, in accordance with the present invention, the Fe-based soft magnetic glassy alloy may be composed of, in atomic percentage, aluminum: 1 to 10, gallium: 0.5 to 4, phosphorus: 0 to 15, carbon: 2 to 7, boron: 2 to 10, silicon: 0 to 15, and iron: the balance, and incidental impurities may be contained.

[0040] Also, in order to have a larger ΔT_x in a supercooled liquid region, with respect to the compositions described above, if phosphorus is set at 6 to 15 atomic percent and carbon is set at 5 to 7 atomic percent, ΔT_x in a supercooled liquid region of 35°C or more can be obtained.

[0041] Also, the compositions described above may further include germanium, 0 to 4 atomic percent, and preferably, 0.5 to 4 atomic percent.

[0042] Also, the compositions described above may further include 7 atomic percent or less of at least one member selected from the group consisting of niobium, molybdenum, hafnium, tantalum, tungsten, zirconium, and chromium, and also, may include at least one of the elements nickel and cobalt, at 0 to 10 atomic percent and 0 to 30 atomic percent, respectively.

[0043] The thin ribbon 3 composed of the Fe-based soft magnetic glassy alloy, in accordance with the present invention, is produced by casting after a master alloy is molten, or by quenching by means of a single roll or dual rolls, or further by an in-rotating-liquid spinning process or a solution extraction process. By the quenching process, the thin ribbon 3 composed of the Fe-based soft magnetic glassy alloy 3 can have a thickness and a size of more than twice those of the known Fe-based or Co-based amorphous alloys, and by the casting process, more than ten times.

[0044] The Fe-based soft magnetic glassy alloy obtained in the processes described above has soft magnetism at room temperature. The soft magnetism is further improved by heat treatment at temperatures ranging from 300°C to 500°C, and a high resistivity of 1.5 µΩm or more can be obtained, which enables useful application to magnetic cores.

[0045] Additionally, an optimum cooling rate, which is determined in response to the composition of the alloy, the production process, the size and shape of the product, and the like, may generally be set in a range from 1 to 10⁴°C/s. Practically, the cooling rate may be determined by confirming whether or not such crystal phases as Fe₃B, Fe₂B, Fe₃P or the like precipitate in the glassy phase.

[0046] The laminated magnetic cores 1 and 11 are provided with the magnetic core body 4 or the magnetic core body 13, in which the thin ribbon 3 composed of the Fe-based soft magnetic glassy alloy is toroidally wound or laminated. The Fe-based soft magnetic glassy alloy has a temperature difference ΔT_x of a supercooled liquid of 20°C or more, or more preferably 35°C or more, ΔT_x being expressed by the equation, ΔT_x = T_x - T_g (where, T_x is the crystallization temperature and T_g is the glass transition temperature). Thus, the laminated magnetic cores 1 and 11 can be fabricated with a thin ribbon that is thick and the lamination factor of the laminated magnetic cores 1 and 11 can be increased, enabling miniaturization. Also, because of higher resistivity in comparison with the conventional amorphous alloy, low core loss in a high-frequency band can be achieved.

[0047] Also, the Fe-based soft magnetic glassy alloy can be produced not only by the liquid quenching process but also by the casting process, the cost of producing the laminated magnetic cores 1 and 11 can be reduced.

[0048] Also, the Fe-based soft magnetic glassy alloy in accordance with the present invention contains a metallic element other than Fe and a metalloid element, and since it particularly contains silicon, the temperature difference ΔT_x of a supercooled liquid can be increased, and thus, the laminated magnetic cores 1 and 11 can be fabricated with a thin ribbon that is thick, the lamination factors of the laminated magnetic cores 1 and 11 are improved, and the core loss is reduced.

[0049] Also, the laminated magnetic cores 1 and 11 in accordance with the present invention are provided with the magnetic core bodies 4 and 13 composed of the Fe-based soft magnetic glassy alloy having a composition, in atomic percentage, of aluminum: 1 to 10, gallium: 0.5 to 4, phosphorus: 0 to 15, carbon: 2 to 7, boron: 2 to 10, and iron: the balance, or aluminum: 1 to 10, gallium: 0.5 to 4, phosphorus: 0 to 15, carbon: 2 to 7, boron: 2 to 10, silicon: 0 to 15, and iron: the balance, and having a large thickness, high permeability, low coercive force, high saturation magnetic flux density, and excellent soft magnetism, and thus, core loss can be reduced.

[0050] Next, an embodiment which uses a bulk magnetic core will be described. A toroidal magnetic core body is formed by sintering the powder of the Fe-based soft magnetic glassy alloy, or by pouring a molten Fe-based soft magnetic glassy alloy into a given mold and cooling it to solidify, and the magnetic core body obtained is insulation protected by resin-coating, for example, with an epoxy resin, or by encapsulating in a resin case to produce a bulk magnetic core.

[0051] Also, in order to fabricate an EI-shaped bulk magnetic core, an E-shaped core and an I-shaped core are formed by sintering the powder of the Fe-based soft magnetic glassy alloy, and then, these cores are joined together to form a magnetic core body.

[0052] The required portion of such a magnetic core body is resin-coated, for example, with an epoxy resin, or is insulation protected by encapsulating in a resin case to produce an EI-shaped bulk magnetic core.

[0053] FIG. 3 shows an example of a toroidal bulk magnetic core. A bulk magnetic core 20 includes a magnetic core body 22, which is formed by sintering the powder of the Fe-based soft magnetic glassy alloy or by pouring a molten Fe-based soft magnetic glassy alloy into a given mold and cooling so that it solidifies, placed in a hollow toroidal resinous case 21 for containing the magnetic core body.

[0054] The case 21 is formed preferably by using a resin such as a polyacetal resin or a polyethylene terephthalate resin.

[0055] Also, an adhesive 23 is applied onto two spots at the bottom 21a of the case 21 for stably fixing the magnetic core body 22 and the case 21. Preferably, the number of spots onto which the adhesive is applied ranges from 2 to 4.

[0056] As the adhesive 23, an epoxy resin, silicone rubber, or the like is used.

[0057] Next, a method for fabricating the bulk magnetic core 20 in accordance with the present invention by the plasma sintering process will be described.

[0058] FIG. 4 shows the key portion of an example of a plasma sintering apparatus which is suitable for producing the bulk magnetic core 20 in accordance with the present invention. The plasma sintering apparatus basically includes a cylindrical die 30, an upper-punch 31 and a lower-punch 32 which are inserted into the die 30, a punch electrode 33 for supporting the lower-punch 32 and functioning as one of the electrodes for passing a pulse current, a punch electrode 34 for pressing down the upper-punch 31 and functioning as the other electrode for passing the pulse current, and a thermocouple 36 for measuring the temperature of the powder material 35 sandwiched between the upper-punch 31 and the lower punch 32.

[0059] A mold corresponding to the shape of the magnetic core body to be produced is formed on each of the opposing surfaces of the upper-punch 31 and the lower-punch 32.

[0060] Also, the key portion of the plasma sintering apparatus is placed in a chamber (not shown in the drawing). The chamber is connected to a vacuum unit and an atmospheric gas feeder (not shown in the drawing) so that the powder material 35 enclosed between the upper-punch 31 and the lower-punch 32 can be retained in a desired atmosphere such as an inert gas atmosphere.

[0061] In order to produce the bulk magnetic core 20 by using the plasma sintering apparatus having the structure described above, a powder material for molding is prepared. The powder material 35 is produced by casting after an Fe-based soft magnetic glassy alloy having a given composition that will be described below is molten, or by quenching by means of a single roll or dual rolls, or further by the in-rotating-liquid spinning process or the solution extraction process, or by the high-pressure gas spraying process to form into various shapes such as a bulk, a ribbon, linear, and powder, and for a material other than powder, by powdering.

[0062] Next, the prepared powder material 35 is placed between the upper and lower punches 31 and 32 shown in FIG. 4, vacuum is provided in the chamber, and forming is performed by pressurizing with the upper and lower punches 31 and 32, and at the same time, by applying a pulse current such as that shown in FIG. 5, onto the powder material 35 to heat, and thus, the magnetic core body 22 having a desired shape is formed.

[0063] In the plasma sintering process, the temperature of the powder material 35 can be quickly raised at a given rate by the applied electrical current, and the temperature of the powder material 35 can be strictly controlled in response to the value of the applied electrical current, and thereby, in comparison with heating by a heater or the like, the temperature control can be performed much more accurately, enabling sintering almost under the ideal conditions which have been designed in advance.

[0064] In accordance with the present invention, although the required sintering temperature is 300°C or more for solidification, since the Fe-based soft magnetic glassy alloy used as the powder material 35 has a large temperature ΔT_x (T_x - T_g) of a supercooled liquid, the magnetic core body 22 with high density can be obtained by sintering with pressure in this temperature range.

[0065] However, if the sintering temperature is close to the crystallization temperature, magnetic anisotropy occurs because of crystal nucleation (structural short range ordering) and crystal precipitation, and thereby, soft magnetism may deteriorate.

[0066] Also, from the mechanism of the plasma sintering apparatus, the sintering temperature being monitored is the temperature of the thermocouple 36 mounted onto the die 30, which is lower than the heating temperature of the powder material 35.

[0067] Therefore, the sintering temperature in accordance with the present invention is preferably in a range which satisfies the relationship, T ≤ T_x, where T_x is the crystallization temperature and T is the sintering temperature.

[0068] Also, in particular, when silicon is added into the Fe-based soft magnetic glassy alloy, the crystallization temperature T_x rises and the temperature difference ΔT_x of a supercooled liquid increases, resulting in a more thermally stable amorphous material. Thereby, by powdering the Fe-based soft magnetic glassy alloy and sintering with pressure, the magnetic core body 22 having higher density can be obtained in comparison with a case in which a powder material that does not contain silicon is used.

[0069] In accordance with the present invention, the heating rate is preferably set at 40°C/minute or more when sintering is performed because the crystal phase is generated at a slower heating rate.

[0070] Also, pressure during sintering is preferably set at 3 t/cm² or more because a magnetic core body cannot be formed with excessively low applied pressure.

[0071] Also, heat treatment may be performed on the magnetic core body 22, and thus, magnetic properties can be enhanced. In such a case, heat-treating temperature is set higher than Curie temperature and lower than the temperature at which crystal precipitation that deteriorates magnetic properties occurs, and specifically, preferably, set at 300 to 500°C, and more preferably, set at 300 to 450°C.

[0072] Since the magnetic core body 22 produced as described above has the same composition as that of the Fe-based soft magnetic glassy alloy used as the powder material 35, it has excellent soft magnetism at room temperature, more excellent soft magnetism by heat treatment, and, in particular, a high resistivity of 1.5 µΩm or more.

[0073] Accordingly, since the bulk magnetic core 20 including the magnetic core body 22 has excellent soft magnetism, it is widely applicable to magnetic cores of transformers, choke coils, magnetic sensors, and the like, resulting in a magnetic core having superior characteristics in comparison with the conventional material.

[0074] Although the method of forming the powder material 35 composed of the Fe-based soft magnetic glassy alloy by the plasma sintering process is described in the above, the method is not limited to this, and the bulk magnetic core body 3 may be produced by sintering with pressure by means of extrusion or the like.

[0075] Furthermore, the bulk magnetic core 20 in accordance with the present invention can be obtained by including the magnetic core body 22 which is produced by pouring a molten Fe-based soft magnetic glassy alloy into a given mold and cooling it to solidify.

[0076] In order to obtain the molten Fe-based soft magnetic glassy alloy, after predetermined amounts of iron, aluminum, gallium, an Fe-C alloy, an Fe-P alloy and boron are weighed as raw materials, these materials are molten in a low pressure argon atmosphere by means of a high-frequency induction furnace, an arc furnace, a crucible furnace, a reverberatory furnace, or the like.

[0077] Then, the molten alloy is poured into a given mold and slowly cooled to solidify it, and thus, the magnetic core body 22 in a desired shape can be obtained.

[0078] Since the magnetic core body 22 obtained as described above has high density and excellent soft magnetism, the same as those of the magnetic core body produced by sintering alloy powder, it can be used for a magnetic core of transformers, choke coils, magnetic sensors, and the like.

[0079] In accordance with the bulk magnetic core 20 described above, the bulk magnetic core body 22 is produced by sintering the powder of the Fe-based soft magnetic glassy alloy by the plasma sintering process. The Fe-based soft magnetic glassy alloy has a temperature difference ΔT_x of a supercooled liquid of 20°C or more, or more preferably 35°C or more, ΔT_x being expressed by the equation, ΔT_x = T_x - T_g (where, T_x is the crystallization temperature and T_g is the glass transition temperature). Since the bulk magnetic core body 22 having high resistivity and high density can be obtained, core loss can be reduced.

[0080] Also, in accordance with the bulk magnetic core 20 described above, since the sintering temperature is set in a temperature range which satisfies the relationship, T ≤ T_x, where T_x is the crystallization temperature and T is the sintering temperature, the magnetic core body 22 having the same composition as that of the Fe-based soft magnetic glassy alloy as raw material, high saturation magnetic flux density, and excellent permeability can be obtained. Thereby, core loss can be reduced.

[0081] Furthermore, by heat treating, the sintered magnetic core body 22 has higher saturation magnetic flux density and more excellent permeability.

[0082] Also, in accordance with the bulk magnetic core 20 described above, the magnetic core body 22 can be produced not only by the plasma sintering process but also by the casting process in which the molten alloy is solidified by cooling, and thus, the production cost of the bulk magnetic core 20 can be reduced.

[0083] Also, the Fe-based soft magnetic glassy alloy in accordance with the present invention contains a metallic element other than Fe and a metalloid element, and since it particularly contains silicon, a temperature difference ΔT_x of a supercooled liquid can be increased. Thereby, it is possible to raise the sintering temperature when the alloy powder is sintered, and the magnetic core body 22 having higher density can be obtained, resulting in a decrease in core loss of the bulk magnetic core 20.

[0084] Also, the bulk magnetic core 20 in accordance with the present invention is provided with the magnetic core body 22 composed of the Fe-based soft magnetic glassy alloy having a composition, in atomic percentage, of aluminum: 1 to 10, gallium: 0.5 to 4, phosphorus: 0 to 15, carbon: 2 to 7, boron: 2 to 10, and iron: the balance; or aluminum: 1 to 10, gallium: 0.5 to 4, phosphorus: 0 to 15, carbon: 2 to 7, boron: 2 to 10, silicon: 0 to 15, and iron: the balance, and having high permeability, low coercive force, high saturation magnetic flux density, and excellent soft magnetism, and thus, core loss can be reduced.

EXAMPLE 1

[0085] Predetermined amounts of iron, aluminum, gallium, an Fe-C alloy, an Fe-P alloy and boron were weighed as raw materials, and these materials were molten in a low pressure argon atmosphere by means of a high-frequency induction furnace to produce a master alloy.

[0086] The master alloy was molten in a crucible, and a quenched thin ribbon having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄ was obtained in the low pressure argon atmosphere by a single roll method in which the molten metal was injected through a nozzle of the crucible onto a rotating roll and quenched. By properly adjusting the nozzle hole diameter of the crucible, the distance (gap) between the nozzle tip and the roll surface, the rotational frequency of the roll, the injection pressure, and the atmospheric pressure, thin ribbon samples having a thickness of 35 to 229 µm were obtained.

[0087] With respect to the thin ribbon samples described above, magnetic properties were evaluated in a case in which heat treatment was performed at temperatures ranging from 300 to 450°C. The heat treatment was performed by using an infrared image furnace, in a vacuum, at a heating rate of 180°C/minute, and temperature retention of 10 minutes.

[0088] FIG. 6 illustrates the dependence of magnetic properties on heating temperature with respect to the individual thin ribbon samples. Also, FIG. 7 illustrates extracts of data shown in FIG. 6.

[0089] As shown in the drawings, the saturation magnetization (σ_s) of the thin ribbon samples having a thickness of 35 to 180 µm had substantially constant values up to 400°C, the same as those of the as-quenched samples (without heat treating), however, it deteriorated when heat treated at 450°C. On the other hand, with respect to the thin ribbon sample having a thickness of 229 µm, the saturation magnetization was at a peak at 400°C, and thereafter deteriorated. The reason for this is considered to be that crystals such as Fe₃B had grown at a temperature of 400°C or more.

[0090] With respect to the as-quenched thin ribbon samples, which were in the amorphous single phase, having thicknesses up to 125 µm, the coercive force (H_c) had substantially constant values, and with respect to those having a larger thickness, the coercive force (H_c) increased. Also, by heat treating, it decreased up to 400°C.

[0091] Next, with respect to the as-quenched thin ribbon samples, which were in the amorphous single phase, having thicknesses of up to 135 µm, the permeability µ'(1 kHz) was substantially constant, and with respect to those having a larger thickness, the permeability µ'(1 kHz) decreased. The heat treating effect improved up to 400°C, however, it widely deteriorated by the heat treatment at 450°C. Also, as the thickness increased, the effect decreased.

[0092] Presumably the change in soft magnetism by the heat treatment occurs because the internal stress in the as-quenched thin ribbon sample is relaxed by the heat treatment. Also, the optimum heat treating temperature T_a is about 350°C in this example.

[0093] Also, heat treatment at a temperature lower than a Curie temperature T_c may cause deterioration of soft magnetism due to the fixation of the magnetic domain, and thus the heat treating temperature should be at least 300°C.

[0094] Also, the heat treatment at 450°C deteriorates soft magnetism in comparison with the as-quenched thin ribbon samples. The deterioration occurred at a temperature close to the crystallization temperature (approximately 500°C) presumably because of domain wall pinning caused by crystal nucleation (structural short range ordering) or crystal precipitation. Accordingly, it has been found that the heat treating temperature preferably ranges from 300 to 500°C, that is, between 300°C and the crystallization temperature, and more preferably from 300 to 450°C.

[0095] Also, with respect to the thin ribbon samples in example 1, the saturation magnetization (σ_s), the coercive force (H_c), the permeability (µ'), the temperature difference (ΔT_x) of a supercooled liquid, and the structure are summarized in Table 1. The structure was analyzed by an X-ray diffraction method (XRD), and also, amo represents an amorphous single phase, and amo + cry represents a structure including an amorphous phase and a crystal phase.

[0096] The ΔT_x was a substantially constant (ΔT_x = 47°C), except for the sample having a thickness of 229 µm.

[0097] FIG. 8 shows the dependence of saturation magnetization (σ_s), coercive force (H_c) and permeability (µ') on thickness with respect to an as-quenched comparative sample having a composition of Fe₇₈Si₉B₁₃, the comparative sample after heat treating at 370°C for 120 minutes, the as-quenched thin ribbon sample in the example 1, and the thin ribbon sample after heat treating at 350°C for 10 minutes.

[0098] In all of the above samples, magnetic properties did not deteriorate significantly, and excellent properties were obtained, when the thickness ranged from 30 to 200 µm.

[0099] FIG. 9 shows the results of measuring fracture strain by means of a bending test with respect to a comparative sample having a composition of Fe₇₈S1₉B₁₃ after heat treating at 370°C for 120 minutes, and a sample having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄ after heat treating at 350°C for 10 minutes.

[0100] The bending test was performed by using two rods and thin ribbon samples. A thin ribbon placed parallel to the rods was sandwiched between the tips of the two rods, the two rods were gradually brought close to each other to bend the thin ribbon into a mountain-like shape. A value of t/(L - t) was defined as fracture strain (λf), where L is a width between the tips of the rods and t is a thickness of the thin ribbon when the thin ribbon was broken by bending as described above.

[0101] As shown in FIG. 9, the bending strength of comparative sample having a composition of Fe₇₈Si₉B₁₃ decreases sharply (i.e., is easily broken) as the thickness increases. On the other hand, the bending strength of sample having the composition in accordance with the present invention does not decrease easily (i.e., is not easily broken) even when the thickness increases. Also, it has been found that in a case in which the thickness is 60 µm or more, the sample having the composition in accordance with the present invention has greater bending strength in comparison with the comparative sample.

[0102] Accordingly, when the alloy thin ribbon having a composition in accordance with the present invention is toroidally wound to form a laminated magnetic core, the curvature radius can be reduced, resulting in a small-sized laminated magnetic core.

[0103] FIG. 10 shows the results of measuring the dependence of resistivity on thickness with respect to a comparative sample having a composition of Fe₇₈Si₉B₁₃ and a sample having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄.

[0104] The sample in accordance with the present invention had higher resistivity in comparison with the comparative sample, and had a resistivity of 1.5 µΩm or more with respect to the samples having thicknesses ranging from 18 µm to 235 µm. Accordingly, it has been found that the sample in accordance with the present invention can provide a laminated magnetic core having low eddy current loss in high frequency and low high-frequency loss.

EXAMPLE 2

[0105] Next, regarding a composition of Fe_70+xAl₅Ga₂(P₅₅C₂₅B₂₀)_23-x, thin ribbon samples were produced by changing the Fe content, and the structure and the properties of each thin ribbon sample were observed. The thin ribbon samples were produced similarly to the example 1 described above, and the thickness of the samples was set at 30 µm.

[0106] FIG. 11 shows the results of the measuring magnetic properties of each thin ribbon sample (as-quenched). Also, the values of saturation magnetization (σ_s), coercive force (H_c) and permeability (µ') of the known Fe-Si-B-system amorphous material (with a thickness of 25 µm, and after heat treating in a vacuum at 370°C for 120 minutes) as a comparative sample are shown in dotted lines in the drawing.

[0107] As is clear from the drawing, saturation magnetization (σ_s) improved as the Fe content increased. Also, in an Fe content range having an amorphous single phase structure, when the Fe content was at 75 atomic percent, a value, σ_s = 150 emu/g, which was substantially the same as that of the Fe-Si-B-system comparative sample (σ_s = 183 emu/g) was obtained. The coercive force H_c was substantially constant in the samples having the Fe content of up to 75 atomic percent which had an amorphous single phase structure, and with an Fe content higher than the above, coercive force H_c greatly increased.

[0108] Although permeability (µ'(1 kHz)) decreased as the Fe content increased, with the Fe content in a range of 70 to 76 atomic percent, excellent soft magnetism having a permeability of 5,000 or more was obtained.

[0109] As a result, it has been confirmed that in the Fe-based soft magnetic glassy alloy in accordance with the present invention, by increasing iron, saturation magnetization (σ_s) can be improved, and with a composition of Fe₇₅Al₅Ga₂P_9.9C_4.5B_3.6, an Fe-based soft magnetic glassy alloy having the substantially same σ_s as that of the known Fe-Si-B-system amorphous material can be obtained by the single roll liquid quenching process.

EXAMPLE 3

[0110] Next, with reference to an example of an Fe-based soft magnetic glassy alloy having the composition described in the example 1 to which silicon is added, the effect will be clarified.

[0111] An ingot having an atomic composition of Fe₇₂Al₅Ga₂P₁₀C₆B₄Si₁ was produced and molten in a crucible, and a quenched thin ribbon was obtained in an argon atmosphere by the single roll method in which the molten metal was injected through a nozzle of the crucible onto a rotating roll and quenched. By setting the nozzle hole diameter at 0.4 to 0.5 mm, the distance (gap) between the nozzle tip and the roll surface at 0.3 mm, the rotational frequency of the roll at 200 to 2,500 r.p.m., the injection pressure at 0.35 to 0.40 kgf/cm², the atmospheric pressure at - 10 cmHg, and the roll surface state # 1000 as the production conditions, thin ribbons having thicknesses ranging from 20 to 250 µm were produced.

[0112] With respect to the thin ribbon samples having thicknesses ranging from 20 to 250 µm described above, magnetic properties were evaluated in cases without heat treating (as-quenched) and after heat treating. FIG. 12 shows the dependence of magnetic properties on thickness with respect to each thin ribbon sample. The heat treatment was performed by using an infrared image furnace, in a vacuum, at a heating rate of 180°C/minute, a retention temperature of 350°C, and a retention time of 30 minutes, which were optimum conditions for the samples without silicon in the example 1 described above.

[0113] As is clear from the drawing, saturation magnetization (σ_s) had a substantially constant value of approximately 145 emu/g, regardless of thickness, in the case without heat treatment. Saturation magnetization (σ_s) after heat treatment did not significantly differ from that without heat treatment, up to a thickness of 160 µm having an amorphous single phase structure, however, with a thickness larger than the above, the saturation magnetization (σ_s) deteriorated in comparison with that without heat treatment. The reason for this is considered to be that crystals such as Fe₃B and Fe₃C had grown by heat treating.

[0114] With respect to the as-quenched samples, coercive force (H_c) increased as thickness increased. Also, with respect to the samples after heat treating, coercive force (H_c) decreased in comparison with the as-quenched samples, in a range from 0.625 to 0.125 Oe, in any of the thicknesses.

[0115] Presumably coercive force (H_c) decreased by heat treating because the internal stress in the as-quenched sample was relaxed by the heat treatment.

[0116] Permeability (µ'(1 kHz)) decreased as thickness increased with respect to the as-quenched samples. Also, by heat treating, the permeability µ' improved and reached to the substantially same value as that of the Fe-based soft magnetic glassy alloy having the composition without silicon in the example 1 described above. The heat treating effect decreased as thickness increased in this example, the same as that in the example 1. However, even at a thickness of 200 µm, permeability, after heat treatment, was 5,000 or more, which is sufficient for practical use.

[0117] With respect to the samples (as-quenched) having different thicknesses in this example, the saturation magnetization (σ_s), the coercive force (H_c), the permeability (µ'), the temperature difference (ΔT_x) of a supercooled liquid, and the structure are summarized in Table 2.

[0118] FIG. 13 shows the results of measuring the dependence of the saturation magnetization (σ_s), the coercive force (H_c), and the permeability (µ') on thickness with respect to a comparative sample having a composition of Fe₇₈Si₉B₁₃ after heat treating at 370°C for 120 minutes, and a sample having a composition of Fe₇₂Al₅Ga₂P₁₀C₆B₄Si₁ after heat treating at 350°C for 30 minutes.

[0119] From the results, it has been confirmed that the Fe-based soft magnetic glassy alloy samples with a composition of Fe₇₂Al₅Ga₂P₁₀C₆B₄Si₁ in accordance with the present invention have less deterioration in magnetic properties and excellent properties, in a thickness range from 20 to 250 µm, in comparison with the known comparative samples with a composition of Fe₇₈Si₉B₁₃.

[0120] In particular, with respect to soft magnetism, the samples in accordance with the present invention have superior permeability to the conventional material, and in a thickness range of 20 to 250 µm, excellent soft magnetism with permeability of 5,000 or more is obtainable.

EXAMPLE 4

[0121] Predetermined amounts of iron, aluminum, gallium, an Fe-C alloy, an Fe-P alloy and boron, and also silicon as required were weighed as raw materials, and these materials were molten in a low pressure argon atmosphere by means of a high-frequency induction furnace to produce a master alloy.

[0122] The master alloy was molten in a crucible, and quenched thin ribbons having compositions of Fe₇₃Al₅Ga₂P₁₁C₅B₄, Fe₇₀Al₅Ga₂P_9.65C_5.75B_4.6Si₃, Fe₇₂Al₅Ga₂P₁₀C₆B₄Si₁, Fe₇₀Al_3.57Ga_1.43P_13.8C_6.25B₅, and Fe₇₇Al_2.14Ga_0.86P_8.4C₅B₄Si_2.6 were obtained in the low pressure argon atmosphere by a single roll method in which the molten metal was injected through a nozzle of the crucible onto a rotating roll and quenched. By properly adjusting the nozzle hole diameter of the crucible, a distance (gap) between the nozzle tip and the roll surface, the rotational frequency of the roll, injection pressure, and atmospheric pressure, thin ribbons having a thickness of 25 to 229 µm were obtained.

[0123] Next, the individual thin ribbons were press-cut into rings, the required number of rings was laminated, and after silicone rubber was impregnated into spaces between layers for insulating and fixing each layer, toroidal laminated magnetic cores having an outer diameter of 8 mm, an inner diameter of 4 mm, and a thickness of 5 mm, as shown in FIG. 2, were produced.

[0124] The lamination factor measured is shown in Table 3 with respect to the laminated magnetic cores produced from the quenched thin ribbons having compositions of Fe₇₃Al₅Ga₂P₁₁C₅B₄ (thickness 50 µm), Fe₇₂Al₅Ga₂P₁₀C₆B₄Si₁ (thickness 100 µm), and Fe₇₀Al₅Ga₂P_9.65C_5.75B_4.6Si₃ (thickness 200 µm).

[0125] Also, FIG. 14 shows the relationship between thickness and lamination factor with respect to the laminated magnetic cores having the shape and size described above produced from the quenched thin ribbons having a composition of Fe₇₇Al_2.14Ga_0.86P_8.4C₅B₄Si_2.6 with various thicknesses.

[0126] The lamination factor was measured by observing the cross-section of the laminated magnetic core by means of a microscope.

[0127] As shown in FIG. 14, the lamination factor increases as thickness increases, and if thickness exceeds 100 µm, the lamination factor will have a substantially constant value of 97% or more. In the laminated magnetic core including the Fe-based soft magnetic glassy alloy in accordance with the present invention, soft magnetism does not deteriorate as described above even if the thickness of the thin ribbon exceeds 100 µm, and thus, core loss can be reduced.

[0128] On the other hand, the known amorphous alloy of Fe₇₈Si₉B₁₃ can only have a thickness of approximately 20 µm and a low lamination factor of 87%.

[0129] Since the known amorphous alloy has a small temperature difference ΔT_x in a supercooled liquid region, when a molten alloy having a predetermined composition is quenched by the liquid quenching process to produce a thin ribbon, the thickness of the thin ribbon must be 50 µm or less in order not to decrease soft magnetism, and if the thickness exceeds the above, soft magnetism deteriorates, and thereby, increase in the lamination factor and improvement in soft magnetism cannot be achieved at the same time, and a laminated magnetic core having low core loss cannot be obtained.

TABLE 3

Alloy composition	Thickness (µm)	Lamination factor (%)
Fe73Al5Ga2P11C5B4	50	94
Fe72Al5Ga2P10C6B4Si1	100	97
Fe70Al5Ga2P9.65C5.75B4.6Si3	200	98
Fe78Si9B13	20	87

[0130] Furthermore, with respect to the laminated magnetic cores produced from the alloy thin ribbons having the compositions of Fe₇₃Al₅Ga₂P₁₁C₅B₄ and Fe₇₇Al_2.14Ga_0.86P_8.4C₅B₄Si_2.6 and the alloy having a composition of Fe₇₈Si₉B₁₃ (comparative example), with various thicknesses, the dependence of core loss (W), permeability (µ_e, real value), coercive force (H_c), and saturation magnetic flux density (B_g) on thickness was evaluated. The results are shown in FIG 15.

[0131] Also, FIG. 16 shows the dependence of core loss (W) on thickness, including the data of a laminated magnetic core produced from a thin ribbon of silicon steel (Si 6.5%) as comparative example.

[0132] In FIG. 15, the laminated magnetic core having a composition of Fe₇₇Al_2.14Ga_0.86P_8.4C₅B₄Si_2.6 has the substantially same saturation magnetic flux density (B_s) as that of the laminated magnetic core having a composition of Fe₇₈Si₉B₁₃. Presumably the laminated magnetic core having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄ has low magnetic flux density because of a slightly lower Fe content. With respect to the laminated magnetic cores as examples, the coercive force does not depend on thickness, however, with respect to the laminated magnetic core having a composition of Fe₇₈Si₉B₁₃, as the thickness of the thin ribbon increases, the coercive force increases, which reveals the deterioration in soft magnetism.

[0133] The permeability (real value) of the laminated magnetic cores as examples slightly decreases as the thickness of thin ribbons increase. On the other hand, in the laminated magnetic core having a composition of Fe₇₈Si₉B₁₃ as comparative example, the permeability (real value) deteriorates more greatly as the thickness of the thin ribbon increases.

[0134] Also, regarding core loss, in FIGs. 13 and 14, with respect to the laminated magnetic core having a composition of Fe₇₈Si₉B₁₃ as comparative example, if the thickness of the thin ribbon exceeds 50 µm, core loss sharply increases. Also, with respect to the laminated magnetic core composed of silicon steel as another comparative example, core loss does not depend on the thickness of the thin ribbon, and is substantially constant, however, it is higher than that of the laminated magnetic core as example.

[0135] As described above, the Fe-based soft magnetic glassy alloy in accordance with the present invention has a larger temperature difference in a supercooled liquid region than that of the known amorphous alloy (Fe₇₈Si₉B₁₃), and a thick bulk can be obtained, enabling an increase in the lamination factor of the laminated magnetic core and a decrease in core loss of the laminated magnetic core.

[0136] The present invention is not limited to the examples described above, and, of course, the invention may be applied to various other modes with respect to the composition, production method, heat treating conditions, shapes, and the like.

EXAMPLE 5

[0137] Predetermined amounts of iron, aluminum, gallium, an Fe-C alloy, an Fe-P alloy and boron were weighed as raw materials, and these materials were molten in a low pressure argon atmosphere by means of a radio-frequency induction, heating apparatus to produce an ingot having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄ in atomic percentages.

[0138] The ingot was molten in a crucible, and a quenched thin ribbon having an amorphous single phase structure was obtained in a low pressure argon atmosphere by a single roll method in which the molten metal was injected through a nozzle of the crucible onto a rotating roll and quenched. The quenched thin ribbon was crushed into powder in the open air by means of a rotor mill. Powder having a grain size of 53 to 105 µm was selected for use as the powder material in the subsequent process.

[0139] After approximately 2 g of the powder material was filled into a dice composed of tungsten carbide by using a hand press, it was mounted into a die shown in FIG. 4, and the interior of the chamber was pressurized by the upper and lower punches in an atmosphere of 3 x 10^-5 torr while the powder material was heated by applying an pulse current. As shown in FIG. 15, a flow of 12 pulses and a pause of 2 pulses constituted a pulse waveform. The powder material was heated by a current of 4,700 to 4,800 A at maximum.

[0140] Sintering was performed by raising the temperature of the sample from room temperature to the sintering temperature with a pressure of 6.5 t/cm² and by retaining for approximately 5 minutes. The heating rate was 100°C/min.

[0141] The opposing faces of the upper and lower punches Used were not provided with molds. Accordingly, the sinter obtained was toroidal-shaped, with a diameter of 10 mm and a thickness of 2 mm.

[0142] FIG. 17 shows a differential scanning calorimeter (DSC) curve of the powder material produced by crushing the quenched glassy alloy thin film having a composition of Fe₇₃Al₅Ga₂P₁₁C₅B₄, and FIG. 18 shows a DSC curve of a sinter obtained by plasma sintering the powder material at a sintering temperature of 430°C.

[0143] The DSC curve in FIG. 17 demonstrates T_x = 512°C, T_g = 465°C, and ΔT_x = 47°C with respect to the powder material. Since a supercooled liquid region exists in a wide temperature range below the crystallization temperature and the value expressed by the ΔT_x = T_x - T_g is large, it has been confirmed that the alloy having the above composition is highly capable of forming an amorphous structure.

[0144] Also, the DSC curve in FIG. 18 demonstrates T_x = 512°C, T_g = 465°C, and ΔT_x = 47°C with respect to the sinter. The results of FIGs. 17 and 18 confirm that the glassy alloy powder material and the sinter have the same ΔT_x, T_x, and T_g.

[0145] FIG. 19 shows the results of an X-ray diffraction for sinters obtained after the powder material was plasma sintered at sintering temperatures of 380°C, 400°C, 430°C, and 460°C, respectively. The samples sintered at 380°C, 400°C, and 430°C have halo patterns, which confirms that they have an amorphous single phase structure. On the other hand, in the sample sintered at 460°C, a sharply peaked diffraction line is observed, confirming an existence of a crystal phase.

[0146] FIG. 20 shows relationships between the sintering temperature during plasma sintering and the density of a sinter obtained, and the permeability (µ_e), the coercive force (H_c), and the saturation magnetic flux density (B_s) of a bulk material to which heat treatment was performed at 350°C for 15 minutes after sintering.

[0147] As shown in the drawing, the density of the sinter increases as the sintering temperature increases, and by sintering at 430°C or more, a sinter having a high relative density of 99.7% or more is obtained. Incidentally, if the pressure is increased during sintering, a high density sinter can be obtained with a lower temperature.

[0148] With respect to magnetic properties, the coercive force (H_c) is substantially constant at a sintering temperature of up to around 430°C, permeability (µ_e) and saturation magnetic flux density (B_s) improve as the temperature rises, and, in particular, at a sintering temperature of 430°C, excellent soft magnetism is obtained. On the other hand, at a sintering temperature of 460°C, the saturation magnetic flux density decreases, the coercive force increases, and the permeability decreases, resulting in the deterioration in soft magnetism.

[0149] As described above, in accordance with the present invention, by setting the sintering temperature at 430°C or less (that is, in a range which satisfies the relationship, T ≤ T_x, where T_x is the crystallization temperature and T is the sintering temperature), a sinter which has high density, an amorphous single phase structure as sintered, and excellent soft magnetism after heat treatment can be obtained.

EXAMPLE 6

[0150] A powder material was obtained similarly to the example 4, except for an atomic composition being Fe₇₂Al₅Ga₂P₁₁C₆B₄.

[0151] Next the powder material was sintered similarly to the example 4 by means of the plasma sintering apparatus shown in FIG. 4.

[0152] By using the upper and lower punches having predetermined molds formed on the opposing faces, a magnetic core body having an outer diameter of 10 mm, an inner diameter of 6 mm, and a thickness of 2 mm, as shown in FIG. 3, was produced.

[0153] The magnetic core body was placed in a hollow toroidal case composed of a polyacetal resin as shown in FIG. 3. An epoxy resin was applied onto two spots at the bottom of the case for fixing the case and the magnetic core body. Thus, a bulk magnetic core was produced.

[0154] The relationship between magnetic flux density and core loss with respect to the bulk magnetic core in this example is shown in FIG. 21. As comparative example, the relationship between magnetic flux density and core loss with respect to a magnetic core produced by laminating silicon steel sheets (Si 3.5%) is also shown in FIG. 21.

Claims

1. A magnetic core comprising a magnetic core body comprising an Fe-based soft magnetic glassy alloy having a temperature difference ΔT_x of a supercooled liquid of 20 °C or more, ΔT_x being expressed by the equation, ΔT_x = T_x - T_g (where T_x is the crystallization temperature and T_g is the glass transition temperature) and a resistivity of 1.5 µΩm or more, said Fe-based soft magnetic glassy alloy containing at least one metallic element selected from the group consisting of aluminum, gallium, indium, and tin, and at least one metalloid element selected from the group consisting of phosphorus, carbon, boron, germanium, and silicon.

2. A magnetic core according to claim 1, wherein said magnetic core body is fabricated by laminating thin ribbons of said Fe-based soft magnetic glassy alloy, or toroidally winding a thin ribbon of said Fe-based soft magnetic glassy alloy.

3. A magnetic core according to claim 1, wherein said magnetic core body is fabricated by sintering the powder of said Fe-based soft magnetic glassy alloy by a plasma sintering process while heating at a heating rate of 40°C/minute or more.

4. A magnetic core according to claim 1, wherein said magnetic core body is fabricated by cooling to solidify the molten Fe-based soft magnetic glassy alloy.

5. A magnetic core according to claim 1, wherein said Fe-based soft magnetic glassy alloy has the following composition, by atomic percent:

aluminum	1 to 10
gallium	0.5 to 4
phosphorus	0 to 15
carbon	2 to 7
boron	2 to 10
iron	the balance

6. A magnetic core according to claim 1, wherein said Fe-based soft magnetic glassy alloy has the following composition, by atomic percent:

aluminum	1 to 10
gallium	0.5 to 4
phosphorus	0 to 15
carbon	2 to 7
boron	2 to 10
silicon	0 to 15
iron	the balance

Drawing