US 3546030 A
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United States Patent Ofi ice 3,546,030 Patented Dec. 8, 1970 3,546,030 PERMANENT MAGNETS BUILT UP F M R Kurt Heinz Jurgen Buschow and Wilhelmus Antonius Johannes Josephus Velge, Emmasingel, Eindhoven,
Netherlands, assignors, by mesne assignments, to U.S. Philips Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed June 7, 1967, Ser. No. 644,101 Claims priority, application Netherlands, June 16, 1966, 6608335 Int. Cl. H01f 1/08; C22c 19/00, 31/02 U.S. Cl. 148--31.57 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to permanent magnets constituted of fine particles having in themselves permanent magnetic properties. The component of these particles which is essential to these properties is M R, Where M is either Co or a combination of Co with one or more of the elements Fe, Cu, Ni and where R is either La, Th, or a combination of Th with one or more of the elements of the rare earths, or a combination of at least three elements of the rare earths.
Others have measured the magnetic properties of numerous intermetallic compounds of the stoichiometric composition M R. Thus for example, many compounds of the from Co -Z have been examined, where Z is an element of the rare earths which are regarded also to include Y. Of these compounds, the magnetic moments and the temperature dependence of the saturation moments have been measured. Further, the magnetic properties of the compounds Co CnTb, Co NiDy, CdYCo and GdNdCo were determined. All these compounds have a hexagonal structure of the CaCu type.
The present invention is based upon the discovery that in compounds Co R having a similar structure to that of Co Y, the said combination of magnetic properties which causes the compound to be a good raw material for the manufacture of permanent magnets (high uniaxial aniso tropy combined with high saturation magnetization) is obtainable if two conditions are fulfilled With regard to the electron structure of the relevant compound.
First the geometry of the electrons in the Co-ions as compared with that in the compound Co Y must not be essentially changed by R, that is to say the population of the 3-d shell in the Co-ion remain substantially the same.
Secondly, the total magnetic moment of the compound which is built up of contributions of both Co and R must not be detnmentally affected by the contribution of R.
The first condition is generally fulfilled by choosing for R those elements which can form with Co compounds of the relevant structure and which occur as trivalent ions in these compounds. Furthermore Th, Ce and Yb, as well as certain combinations of elements, appear to satisfy the first condition.
The second condition is fulfilled by choosing for R those elements or combinations of elements the total magnetic moments of which are directed in parallel with those of the Co-ions or which do not contribute to the magnetic moment.
When the two conditions are combined there appears to exist for R, in addition to the known elements and combinations of elements, a large number of substitution possibilities. Experiments have shown that of these manifold suitable substitutions for R, only the following elements and combinations of elements with Co can form a compound Co R which can be used with good result (sufliciently high H and (BH) as a raw material for the manufacture of permanent magnets: La, Th, or a combination of Th with one or more of the elements of the rare earths, or combinations of at least three rare earths.
It is possible in these compounds to choose for M, instead of the above-mentioned Co, a combination of Co with one or more of the elements Fe, Ni, Cu. The compounds in which M is such a combination generally have a lower sensitivity to deformation of the coercive force and the saturation magnetization.
The extent to which Fe, or Ni, Co or a combination can be substituted for M while retaining favorable magnetic properties depends upon R and the substituents which have been chosen. Thus it has been found, for example, that if R is La and M is a combination of Co and Fe, no more than 5 at. precent of Fe may be present, Whereas the maximum content of Fe may be at. percent if R is Th. If the Fe-content exceeds the specified percentages, the examples given no longer have the hexagonal structure required, resulting in an abrupt decline in magnetic properties. However, in other examples, the magnetic properties may decline gradually, starting from a certain atomic percentage of the substituent.
The compounds Co La, Co La Sm Th and C0 La Ce Sm for example, satisfy the abovementioned conditions.
The invention also relates to a method of manufacturing a permanent magnet as above described. In this method, a body is first manufactured by melting the component elements to form the compound of R and subsequently cooling the mass. The body is homogenized by annealing in an atmosphere which protects against oxidizing influences, at a temperature which lies as nearly as possible, i.e., immediately, below the melting point. The body is subsequently cooled to room temperature and pulverized. The powder, possibly after annealing, then is formed into a magnetic body by molding, possibly in a magnetic field.
Compounds of the formula M R generally have an incongment melting point. As a result, compounds of R and M other than M R may also occur during solidification. During the annealing of the molding at a temperature which lies just below the melting temperature, all the compounds formed during solidification will be converted into the compound M R, that is to say are homogenized. The temperature is chosen therefore at a maximum inter alia to give the particles the greater possible mobility, which enhances an efficient conversion of other compounds into M R.
The homogenization is followed by cooling to room temperature. This cooling may take place at a low rate if no undesired phases occur during this process. If, however, this should be the case, then in one form of the method according to the invention the body should be quenched to room temperature after homogenization.
The quenching process affords the additional advantage that the body becomes more brittle and this is advantageous with a view to the subsequent pulverization.
The invention may be explained more fully with reference to magnetic properties measured on the following examples of compounds (M R particles) according to the invention all which were made in the aforesaid manner:
The maximum energy product (BH) has been measured on a permanent magnet made from CO La Ce Sm and is 5x10 GausS-OerSted.
What is claimed is:
1. A permanent magnet constituted of fine particles, and having magnetic properties, said particles having as a component which is essential to these properties the compound M R, having a hexagonal crystal structure where M is selected from the group consisting of Co and a combination of Co with at least one element selected from the group consisting of Fe, Cu, Ni and where R is selected from the group consisting of La, Th a combination of about 50% La, about 25% Ce and about 25% Sin, and a combination of Th with up to two of the rare earth elements.
2. A permanent magnet as claimed in claim 1 in which R is a combination of Th and two rare earth elements.
3. A permanent magnet as claimed in claim 1 in which M is Co and R is La.
4. A permanent magnet as claimed in claim 2 in which M is Co and R is La Sm Th 5. A permanent magnet as claimed in claim 1 in which M is Co and R is La Ce Sm References Cited UNITED STATES PATENTS 2,813,789 11/1957 Glaser 123 3,102,0U2 871963 WalIaceet al. 'L. 75 1'52X 3,326,637 6/1967 Holtzberg et al. 75152X 3,342,591 9/1967 Gambino et al. 75152 3,421,889 1/1969 Ostertag et a1 75170 3,424,578 1/1969 Strnat et al. 75213 L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner U.S. Cl. X.R.