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 Hc and the ratio of remanence to saturation magnetization, σr / σs, 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 Tc and the spontaneous magnetization in the vicinity of Tc were determined by the method of thermodynamic parameters. The spontaneous magnetizations on the reduced scale, σs(T) / σs(0), were flatter over the entire temperature range 0≤T/Tc≤1 than was predicted by a recent model for amorphous ferromagnets based on MFT. Tc drops rapidly with increasing P content at high concentrations, and apparently it would vanish at a content well below 33 at.% P.