Magnetic Properties of Gold-Rich Gold-Vanadium Alloys

Abstract

Results of measurements on Au-V alloys are presented. The intermetallic compound ${\mathrm{Au}}_4$V, formed through an order-disorder transformation at 560°C, becomes ferromagnetic at ≈60°K. Above that temperature the susceptibility satisfies a Curie-Weiss law. The induced moment at absolute zero, the effective moment, the transition temperature, and the temperature-independent component of the susceptibility all vary from sample to sample, but typical values are $0.5{\mu }_B$ per V ion, 1.7, 50°K, and 150×${10}^{-6\mathrm{}}$ emu/(g at. wt), respectively. The variation is thought to be due to extreme magnetic hardness coupled with a high degree of crystal imperfection. All results indicate that a model of localization in the molecular-field approximation is adequate to describe the ferromagnetism. In agreement with earlier work, dilute solid solutions of V in Au have temperature-dependent susceptibilities. The susceptibilities are describable by a Curie-Weiss law, with parameters that vary with concentration and heat treatment. Temperature dependence occurs only in the concentration range ≈0.1 to 30 at.% V; the Curie constant reaches a maximum value at 5-10 at.% V. A model is presented which can account for the results observed by assuming that a V ion localizes in Au only if there are no V neighbors within a critical distance. In conclusion, the implications for the possible existence of other ferromagnetic intermetallic compounds are discussed.