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

Abstract

A comprehensive study of the magnetic properties of ${\mathrm{Ni}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{P}}_{\mathit{x}}$ alloys prepared by electrodeposition with 11.5\ensuremath{\le}x\ensuremath{\le}23.2 and by melt quenching with 16.3\ensuremath{\le}x\ensuremath{\le}21.0 was performed for temperatures 4.2\ensuremath{\lesssim}T\ensuremath{\le}300 K in magnetic fields up to H=9 kOe and, for most of the melt-quenched alloys, for T\ensuremath{\ge}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\ensuremath{\gtrsim}17 and very weak itinerant ferromagnetism for x\ensuremath{\lesssim}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\ensuremath{\lesssim}x\ensuremath{\lesssim}17), the observed magnetization was dominated by the contribution of superparamagnetic particles.