Magnetic properties of Co-Cu metastable solid solution alloys

Abstract

Metastable solid solution alloy powders and bulk alloys in the cobalt(Co)-copper(Cu) (10--90 mol % Co) system, which is an almost immiscible system at the ambient state, were prepared by mechanical alloying (MA) and shock compression. All MA-treated powders showed the x-ray diffraction patterns of a single phase of fcc structure. The lattice parameter increases with Cu concentration and is fundamentally on the line with Vegard's law. The magnetization curves of ${\mathrm{Co}}_{x}{\mathrm{Cu}}_{100\ensuremath{-}x}$ $(x=20--80)$ metastable bulk alloys at room temperature showed ferromagnetism, while the one of ${\mathrm{Co}}_{10}{\mathrm{Cu}}_{90}$ system showed paramagnetism. The saturation magnetic moment ${(M}_{s})$ curve versus electron numbers per atom at 0 K was found to be similar to the Slater-Pauling curves of other transition-metal binary systems and decreased with increasing Cu concentration and approached zero at about 28.8 electrons per atom. The magnetoresistance ratio at room temperature increased with Cu content in the ferromagnetic region, while the one of the paramagnetic ${\mathrm{Co}}_{10}{\mathrm{Cu}}_{90}$ alloy was negligibly small.