Structure-dependent ferromagnetism in Au₄V studied under high pressure

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D. D. Jackson,¹ J. R. Jeffries,² Wei Qiu,³ Joel D. Griffith,³ S. McCall,¹ C. Aracne,¹ M. Fluss,¹ M. B. Maple,² S. T. Weir,¹ and Y. K. Vohra³
¹Lawrence Livermore National Laboratory, Livermore, California 94551, USA
²Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, California 92093, USA
³Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35124, USA

Received 2 August 2006; published 1 November 2006

Atambient pressure, ordered Au₄V is metallic and displays ferromagnetism atT_C=45 K. The electrical resistivity has been measured as a functionof temperature from 1 K to 300 K and as a functionof pressure up to 30 GPa using various high-pressure devices. Akink, which is associated with the reduction of scattering dueto the onset of ferromagnetic order, is seen in theelectrical resistance as a function of temperature. With applied pressure,this kink is found to broaden and increase in temperatureat a rate of approximately 2.7 K/GPa. Above ~18 GPa, the broadeningof the kink prohibits accurate determination of T_C; however, uponreducing the pressure, no signatures of ferromagnetism were evident inthe electrical resistivity. Both energy-dispersive (P61 GPa) and angle-dispersive (P27 GPa) x-raydiffraction measurements at room temperature show a gradual transition fromthe body-centered-tetragonal phase of Au₄V to a disordered face-centered-cubic structure.This transition is irreversible and continuous, and the data havebeen fit to a Birch-Murnaghan equation of state. In orderto investigate the origin of the magnetic interactions in Au₄V,we have also measured the electrical resistivity of Au_1−xV_x alloysand determined their Kondo temperatures T_K for x<1%. The pressuredependence of T_K for x=0.5% was measured up to 2.8 GPa,for which the Kondo temperature increases at a rate ofdT_K/dP=6.5 K/GPa. Using the volume dependence of the exchange interaction betweenmagnetic vanadium ions, we find that the pressure-induced increase ofthe Curie temperature in Au₄V can be explained by anincrease in the exchange interaction parameter and the number ofmagnetic nearest neighbors.

URL:	http://link.aps.org/doi/10.1103/PhysRevB.74.174401
DOI:	10.1103/PhysRevB.74.174401
PACS:	72.10.Fk; 64.30.+t; 72.15.-v; 72.80.Ga 72.10.Fk Carrier scattering by point defects, dislocations, surfaces, and other imperfections including Kondo effect 64.30.+t Equations of state of specific substances 72.15.-v Electronic conduction in metals and alloys 72.80.Ga Electrical conductivity of transition-metal compounds YEAR: 2006
KEYWORDS:	gold alloys, vanadium alloys, ferromagnetic materials, high-pressure solid-state phase transformations, electrical resistivity, magnetic structure, X-ray diffraction, crystal structure, equations of state, Kondo effect, exchange interactions (electron), Curie temperature

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