Magnetocrystalline anisotropy measurements on some polycrystalline rare-earth cobalt alloys

The singular point detection (SPD) technique recently developed by Asti and Rinaldi was used for anisotropy field (BA) measurements on a range of polycrystalline rare-earth cobalt alloys. The anisotropy constant, K, , was estimated from magnetization measurements on field-aligned samples and the anisotropy constant, K,, was calculated from the relation:2K, + 4K,BA = - M where Ms is the saturation magnetization. Temperatures from 4.2K sto 300 K were used with pulsed magnetic fields up to 20T.The temperature dependence of B A in YCos was observed to be linear while that in ThCos showed a broad peak around 190K. In NdCo, , BA and K, showed a decrease while K2 showed an increase with decreasing temperature. BA in (Y 1 _x2Cox)Cos for x = 0 to 0.129 showed an increase with x for annealed samples while that for x = 0.05 to 0.129,showed a decrease in the as-east state. The temperature dependence of anisotropy in Ere Co" and Tm, Co, indicated the dominance of the rare-earth sub-lattices in these alloys. Attempts to fit K, (T) with a power law gave powers of 2.2 - 2.5 for these compounds while those for Sm, C gave a power of about 27. The latter however showed an excellent agreement with the model of Carr. Measurements on the Y2 (CoxFel _x) series indicated strong temperature and composition (x) dependences in BA, K, and K2 _ These results can be interpreted in terms of preferential substitution of Fe on different ~o lattice sites. Results on Pr, (Cons FeOA )revealed evidence of a magnetization process of first order and were found to be in good agreement with the theory of first order magnetization rotations. Attempts to prepare 5 : 19 phases (for R = Cc, Pr, Nd, La), were successful only in the case of Ces Co. Even in this alloy, I : 5 and 2 : 7 phases were found to be present. BA vah,es of this alloy as a function of temperature were measured.