Structure-dependent ferromagnetism in Au4V studied under high pressure

At ambient pressure, ordered Au4V is metallic and displays ferromagnetism at T-C=45 K. The electrical resistivity has been measured as a function of temperature from 1 K to 300 K and as a function of pressure up to 30 GPa using various high-pressure devices. A kink, which is associated with the reduction of scattering due to the onset of ferromagnetic order, is seen in the electrical resistance as a function of temperature. With applied pressure, this kink is found to broaden and increase in temperature at a rate of approximately 2.7 K/GPa. Above similar to 18 GPa, the broadening of the kink prohibits accurate determination of T-C; however, upon reducing the pressure, no signatures of ferromagnetism were evident in the electrical resistivity. Both energy-dispersive (P <= 61 GPa) and angle-dispersive (P <= 27 GPa) x-ray diffraction measurements at room temperature show a gradual transition from the body-centered-tetragonal phase of Au4V to a disordered face-centered-cubic structure. This transition is irreversible and continuous, and the data have been fit to a Birch-Murnaghan equation of state. In order to investigate the origin of the magnetic interactions in Au4V, we have also measured the electrical resistivity of Au1-xVx alloys and determined their Kondo temperatures T-K for x < 1%. The pressure dependence of T-K for x=0.5% was measured up to 2.8 GPa, for which the Kondo temperature increases at a rate of dT(K)/dP=6.5 K/GPa. Using the volume dependence of the exchange interaction between magnetic vanadium ions, we find that the pressure-induced increase of the Curie temperature in Au4V can be explained by an increase in the exchange interaction parameter and the number of magnetic nearest neighbors.