Structure-dependent ferromagnetism in ${\mathrm{Au}}_{4}\mathrm{V}$ studied under high pressure

Structure-dependent ferromagnetism in ${Au}_{4} V$ studied under high pressure

D. D. Jackson, J. R. Jeffries, Wei Qiu, Joel D. Griffith, S. McCall, C. Aracne, M. Fluss, M. B. Maple, S. T. Weir, and Y. K. Vohra

Phys. Rev. B 74, 174401 – Published 1 November 2006

Abstract

At ambient pressure, ordered ${Au}_{4} V$ 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 $\sim 18 GPa$ , 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 $(P \leq 61 GPa)$ and angle-dispersive $(P \leq 27 GPa)$ x-ray diffraction measurements at room temperature show a gradual transition from the body-centered-tetragonal phase of ${Au}_{4} V$ 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 ${Au}_{4} V$ , we have also measured the electrical resistivity of ${Au}_{1 - x} V_{x}$ 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 $d T_{K} ∕ d P = 6.5 K ∕ GPa$ . Using the volume dependence of the exchange interaction between magnetic vanadium ions, we find that the pressure-induced increase of the Curie temperature in ${Au}_{4} V$ can be explained by an increase in the exchange interaction parameter and the number of magnetic nearest neighbors.

Received 2 August 2006

DOI:https://doi.org/10.1103/PhysRevB.74.174401

Authors & Affiliations

D. D. Jackson¹, J. R. Jeffries², Wei Qiu³, Joel D. Griffith³, S. McCall¹, C. Aracne¹, M. Fluss¹, M. B. Maple², S. T. Weir¹, 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

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Vol. 74, Iss. 17 — 1 November 2006

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Figure 1
(Color online) (a) The crystal structure of ${Au}_{4} V$ showing both the bct ordered structure and the distorted fcc arrangement of Au (Ref. 24). (b) The designer diamond used for this work. A standard four-probe technique was used, leaving two extra leads for redundancy.Reuse & Permissions
Figure 2
(Color online) $ρ (T)$ normalized at $10 K$ as a function of temperature for 1.1, 5.1, 11.0, 14.3, and $20.7 GPa$ , all collected using a designer diamond in a DAC. The inset shows $d^{2} ρ ∕ d T^{2}$ as a function of temperature $T$ in which the peak was used to locate the Curie temperature, denoted by the downward arrows.Reuse & Permissions
Figure 3
(Color online) (a) Angle-dispersive x-ray diffraction (ADXD) spectra after the integration of the 2D image plates. The $(h k l)$ diffraction peaks characteristic of the tetragonal phase become very weak as pressure increases and do not reappear after downloading the pressure. (b) Energy-dispersive x-ray diffraction (EDXD) spectra of the ${Au}_{4} V$ sample under different pressures up to $61 GPa$ . The (323) diffraction peak associated with the tetragonal phase is suppressed with applied pressure, becoming indistinguishable above $18 GPa$ .Reuse & Permissions
Figure 4
(Color online) The electrical resistivity as a function of temperature for $Au − 0.5 % V$ for various pressures. The minimum in the electrical resistivity at $T_{m i n} \approx 20 K$ for the ambient pressure curve is a hallmark of the Kondo effect. With applied pressure, $T_{m i n}$ is only slightly affected; however, the residual resistivity increases by approximately $7$ % from ambient pressure to $2.8 GPa$ .Reuse & Permissions
Figure 5
(Color online) A semilogarithmic plot of the normalized magnetic component of the electrical resistivity $Δ ρ_{M} (T) ∕ Δ ρ_{M} (0)$ (defined in the text) as a function of temperature for various pressures shows the evolution of the Kondo temperature $T_{K}$ for $Au − 0.5 % V$ . The Kondo temperature is defined as the temperature at which $Δ ρ_{M} (T) ∕ Δ ρ_{M} (0) = 0.8$ (horizontal dashed line), corresponding to a deviation from the higher temperature behavior. The inset shows $T_{K}$ as determined from the above criteria as a function of pressure; the line is a linear fit to the data.Reuse & Permissions
Figure 6
(Color online) (a) The measured equation of state of ${Au}_{4} V$ up to $30 GPa$ at $300 K$ (inset shows data up to $61 GPa$ ) obtained from the x-ray diffraction experiments. The square symbols represent the low-pressure tetragonal phase, the triangle symbols represent the disordered fcc phase for pressure above $18 GPa$ , the diamond symbols represent the disordered fcc phase of the decompressed ${Au}_{4} V$ sample, and the solid curve is the fit to the Birch-Murnaghan third-order equation of state (1). (b) $T_{C}$ with the squares from the piston-cylinder and Bridgman cells and the triangles from the DAC. The two highest-pressure data points are differentiated by open triangles due to the significantly higher uncertainty in assigning a transition temperature at these pressures. (c) The height of the peak observed in $d^{2} ρ ∕ d T^{2}$ . (d) RRR defined as $ρ (T = 200 K) ∕ ρ (T = 10 K)$ , with the upward-pointing triangles indicating increasing pressure in the DAC and the leftward-pointing triangles indicating decreasing (downloading) pressure in the DAC. The shaded area bordered by vertical black lines indicates the region of the broad phase transition; the low- and high-pressure boundaries are determined from EDXD and ADXD measurements, respectively.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Structure-dependent ferromagnetism in ${Au}_{4} V$ studied under high pressure

D. D. Jackson, J. R. Jeffries, Wei Qiu, Joel D. Griffith, S. McCall, C. Aracne, M. Fluss, M. B. Maple, S. T. Weir, and Y. K. Vohra

Phys. Rev. B 74, 174401 – Published 1 November 2006

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Physical Review B

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Structure-dependent ferromagnetism in Au4V studied under high pressure

D. D. Jackson, J. R. Jeffries, Wei Qiu, Joel D. Griffith, S. McCall, C. Aracne, M. Fluss, M. B. Maple, S. T. Weir, and Y. K. Vohra

Phys. Rev. B 74, 174401 – Published 1 November 2006

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Structure-dependent ferromagnetism in ${Au}_{4} V$ studied under high pressure