Magnetic properties of amorphous Co–P alloys

Abstract

Amorphous Co–P alloys with compositions ranging between 18–25 at.% P were prepared by electrodeposition. Their magnetic properties were measured with a vibrating sample magnetometer between 4 and 520 °K in fields up to 8 kOe. The coercive force H_c and the ratio of remanence to saturation magnetization, σ_r / σ_s, of the alloys were several hundred times lower for the amorphous than for their as‐crystallized states. Earlier results indicating sharp increases in initial permeability with annealing, short of crystallization, were confirmed. The magnetic moment per atom, n, from low‐temperature measurements, decreases with increasing P content. In particular, the results at low P content indicate the transfer of four P valence electrons at the dilute limit, while those at >23 at.% P indicate a more rapid decrease of n than was expected from the rigid band model and suggest that n→0 at 32 at.% P. Both T_c and the spontaneous magnetization in the vicinity of T_c were determined by the method of thermodynamic parameters. The spontaneous magnetizations on the reduced scale, σ_s(T) / σ_s(0), were flatter over the entire temperature range 0≤T/T_c≤1 than was predicted by a recent model for amorphous ferromagnets based on MFT. T_c drops rapidly with increasing P content at high concentrations, and apparently it would vanish at a content well below 33 at.% P.