Starting material for permanent magnets

Description

[0001] The invention relates to a hard-magnetic material which comprises neodymium and iron.

[0002] A known material of this type is the Nd₂ Fe₁₄ B having a tetragonal crystal structure. It is known that a substitution of B by C in this compound leads to a greater anisotropy (see, for example, Journal de Physique Colloque C6, supplément au no. 9, T. 46, September, 1985, pages C6-­305/308: "Magnetic anisotropy of Carbon Doped Nd₂Fe₁₄B" by Bolzoni, Leccabue, Pareti and Sanchez). It is stated in this article on page 306 that it was not possible to obtain the tetragonal phase when borium was replaced entirely by carbon.

[0003] It is the object of the invention to provide a hard-­magnetic material having a great crystal anisotropy which comprises only carbon instead of boron and also a comparatively high content of neodymium.

[0004] It has been found that this object can be achieved by means of a substance of the following composition:
(RE_1-xNd_x) Fe₁₄C,
wherein RE is one or more rare earth metals having an atomic number exceeding 61 (for example Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu) and
0.5 ≦ x ≦ 0.80.

[0005] It has been found that the magnetic properties decrease substantially if x < 0.5 or if x > 0.8.

[0006] In all the combinations a carbide having a tetragonal crystal structure is found. The Curie-temperature is between 500 and 600 K. The hard-magnetic materials according to the invention can be obtained in the conventional manner by fusing starting materials suitable for that purpose succeeded by an annealing treatment in a protective gas or another vacuum. A number of materials which were obtained in this manner are collected in the following table which also states the Curie-temperature and the annealing temperature.

Table

Compound	Curie-temperature (K)	Annealing temperature (°C)
TbNdFe₁₄C	560	850
Tb0.5Nd1.5Fe₁₄C	550	800
Dy0.5Nd1.5Fe₁₄C	545	850
LuNdFe₁₄C	530	850

[0007] The magnetic properties are comparable to those of materials on the basis of Nd₂Fe₁₄B or better. The absence of boron is an advantage since now poisonous volatile boron compounds cannot be formed in the preparation.

[0008] Magnets in the form of shaped bodies can be sintered from the resulting material after pulverisation in the manner conventional with Nd₂Fe₁₄B.

Claims

1. A hard-magnetic material which comprises neodymium and iron, characterized in that the material has the composition (RE_1-xNd_x) Fe₁₄C, wherein RE is Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and/or Lu and
0.5 ≦ x ≦ 0.8.

2. A permanent magnet on the basis of a material as claimed in Claim 1.