Magnetism and local environment model in (Ni1-cCoc)0.78P0.14B0.08amorphous alloys

The magnetic properties of amorphous alloys (Ni1-cCoc)0.78P0.14B0.08have been investigated. The samples were prepared by the splat-cooling method. The Curie temperatures have been determined and the magnetization measurements performed for 1.7°K≤ T ≤ 270 and fields up to 70 kOe. Ni0.78P0.14B0.08is paramagnetic, whereas Co0.78P0.14B0.08is ferromagnetic until the crystallization temperature (678°K). The average moment per cobalt atom is1.15 μB. In (Ni1-cCoc)0.78P0.14B0.08the critical concentration for the paramagnetic-ferromagnetic transition isc 0.15, this transition occurs in an inhomogeneous way. The saturation magnetization in the whole concentration range can be interpreted (as for some crystallized alloys and compounds) by a local environment model, when a reasonable short range order is assumed. In such a model the magnetic moment per cobalt atom is related merely to the number of its Co first neighbors nCo. For nCo=0 and 1 the cobalt atom is not magnetic, for nCo= 2 and 3 it carries a small momentμ₁ = 0.50 μBand for nCo> 3 it is magnetic withμ₂ = 1.15 μBas in Co0.78P0.14B0.08; the nickel atoms do not carry a substantial moment in the entire concentration range. These features are comparable to those obtained in some crystalline alloys.