Effect of magnetic field applied along the a-axis on the thermal expansion and first-order transition temperature of single crystal Gd5(Si2Ge2)

Han, M. G., Jiles, David, Paulsen, Jonathan, Snyder, John Evan and Lee, S. J. 2002. Effect of magnetic field applied along the a-axis on the thermal expansion and first-order transition temperature of single crystal Gd5(Si2Ge2). Presented at: American Physical Society March Meeting, Indianapolis, USA, 18-22 March 2002.

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Abstract

The giant magnetocaloric material Gd5(SixGe(1-x))4 is known among other things for its unusual first order simultaneous structural and magnetic transition from monoclinic/paramagnetic to orthorhombic/ferromagnetic over the composition range 0.24< x <0.5. Thermal expansion measurements were made on this material to study the effect of magnetic field on the first order transition using single crystal Gd5(Si2Ge2). A magnetic field was applied along the a-axis with strengths of H = 0 kOe, 10 kOe, 15 kOe, 20 kOe and 25 kOe. Thermal expansion was measured on both heating and cooling. On cooling, the transition temperatures were found to be 267K, 271.6K, 273K, 276K, 278.6K respectively. On heating, the transition temperatures shifted to 269K, 274K, 276K, 279K, 281.5K respectively, showing hysteresis in a first order transition. This hysteresis of 2-3K observed during the cooling and heating cycle, was confirmed by in-situ magnetic force microscopy (MFM). The magnetic field increased the transition temperature by 0.5 K per 1kOe for either cooling or heating. This means that application of a magnetic field can change the Curie temperature for this intriguing intermetallic compound. The key to enhancement of the Curie temperature lies in the suppression of one dimensional vibration of the Gd atoms in the lattice. For Gd in Gd5(Si2Ge2)lattice, the applied magnetic field energy is equal to the change in thermal energy that occurs for one dimensional vibration of the Gd atoms. The magnetic moment on the Gd atoms needed to account for this was calculated to be 7.44Bohr magneton, which compares very well to the established value 7.94Bohr magneton per isolated Gd ion.

Item Type:	Conference or Workshop Item (Paper)
Status:	Unpublished
Schools:	Engineering
Related URLs:	Organisation Organisation
Last Modified:	05 Jan 2018 21:25
URI:	https://orca.cardiff.ac.uk/id/eprint/16686

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