A feasible approach for preparing remanence enhanced NdFeB based permanent magnetic compositesThe magnetocrystalline anisotropy of several intermetallic phases of the type RC06 (R= Y, Ce, Pr, Sm, Yorich and Ce-rich mischmetals) has been investigated, and it is concluded that these alloys are promising candidates for fine-particle permanent magnets. They have extremely high uniaxial anisotropy (K = 5.4 to 7.7 X 10 7 erg/cm 3 ), single easy axis, high saturation (B, = 8500 to 11 200 G) and Curie point (l c =464° to 747°C). Approximate upper limits for the possible energy product lie between 18 and 31.3 MGOe. Experimentally, coercive forces of over 8000 Oe and (BH) max = 5.1 MGOe have been observed in SmC06 merely ground at room temperature. Grinding of YCo. and (Ce-MM) C0 6 produces an increase of MHc to 2200 and 2700 Oe, respectively, followed by a decrease as particle size continues to decrease.
Saturation moments, Curie temperatures, and supporting crystallographic data are reported for a series of ferrimagnetic intermetallic compounds of the stoichiometry R2Co17, where R is any of the rare-earth elements Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The saturation moment of Y2Co17 is 27.2, that of Lu2Co17 is 27.6 Bohr magnetons per formula unit, indicating a cobalt moment of 1.61 μB in this series. Substitution of Pr and Nd for R raises the saturation to 32.8 μB/F.U. for Pr2Co17; all other lanthanides lower it (minimum: 5.7 μB/F.U. for Ho2Co17). Except for Sm2Co17, the values agree well with the concept that the Co moments couple antiparallel with the rare-earth spin sublattice. For Ce and Pr, a valence>3 and electron transfer from R to Co must be assumed. The Curie temperatures lie between 795° and 940°C. The variation of Tc with the atomic number suggests that two coupling mechanisms are active: direct Co-Co exchange interaction and indirect exchange between R and Co via polarized conduction electrons.
The magnetocrystalline constants of two ferromagnetic rare-earth-cobalt intermetallic compounds, YCo5 and Y2Co17, have been measured in the approximate temperature range 20°–300°K. The anisotropy constants were obtained from magnetization vs applied-field curves measured on single-crystal spheres in the principal crystallographic directions of the hexagonal structure. YCo5 has a magnetically easy c axis and no anisotropy in the hard basal plane. K1 increases from 7.03×106 erg/g at 300°K to 10.03×106 erg/g at 24°K. Y2Co17 has an easy basal plane with no anisotropy in the plane. At 307°K, K1=−3.61×105 erg/g, and K2=0.22×105 erg/g while at 21°K, K1=−6.99×105 erg/g and K2=−0.69×105 erg/g.
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