Magnetic properties of electrodeposited, melt-quenched, and liquid Ni-P alloys

A comprehensive study of the magnetic properties of ${\mathrm{Ni}}_{100\mathrm{-}\mathit{x}}$ ${\mathrm{P}}_{\mathit{x}}$ alloys prepared by electrodeposition with 11.5≤x≤23.2 and by melt quenching with 16.3≤x≤21.0 was performed for temperatures 4.2≲T≤300 K in magnetic fields up to H=9 kOe and, for most of the melt-quenched alloys, for T≥300 K including the molten state as well. The individual contributions to the magnetization were identified and determined separately. The matrix of Ni-P alloys was found to exhibit Pauli paramagnetism for x≳17 and very weak itinerant ferromagnetism for x≲14. However, magnetic inhomogeneities in the form of ferromagnetic precipitates, giant-moment paramagnetic clusters and/or superparamagnetic particles could be identified throughout the whole concentration range studied and their amount and character varied significantly with alloy composition and preparation technique. In the paramagnetic phase, the temperature-independent Pauli susceptibility was not sensitive to the way of preparation, it agreed well with extrapolated room-temperature liquid-state data, decreased approximately linearly with increasing P content and extrapolated to the corresponding value of the crystalline stoichiometric compound ${\mathrm{Ni}}_3$P. In the ferromagnetic phase, the magnetization data of the matrix could be reasonably well accounted for in terms of the Stoner-Edwards-Wohlfarth model and the theory of Mathon, yielding 85.7 at. % Ni as the critical concentration for the onset of spontaneous magnetic order. For alloys in the intermediate composition range (14≲x≲17), the observed magnetization was dominated by the contribution of superparamagnetic particles.