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Dresden 2014 – scientific programme

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MA: Fachverband Magnetismus

MA 42: Magnetic Materials III

MA 42.8: Talk

Thursday, April 3, 2014, 17:00–17:15, HSZ 04

Element resolved atomic vibrational properties of magnetocaloric LaFe13−xSix — •Markus Ernst Gruner1,2, Werner Keune2,3, Beatriz Roldan Cuenya4, Joachim Landers2, Sergey Makarov2, David Klar2, Michael Y. Hu5, Ercan E. Alp5, Maria Krautz1, Oliver Gutfleisch6, and Heiko Wende21IFW Dresden — 2Universität Duisburg-Essen — 3MPI Halle — 4Ruhr-Universität Bochum — 5Argonne National Laboratory — 6TU Darmstadt

Large magnetocaloric effects are obtained at discontinuous magnetic phase transitions, which are preferentially close to second-order as this keeps hysteresis losses small. In LaFe13−xSix, the first order character is connected with a significant volume decrease upon disordering the magnetic subsystem, arising from the coupling of magnetic and elastic degrees of freedom. Their contribution to the total entropy change is thus not necessarily cooperative. By comparing nuclear resonant inelastic X-ray scattering (NRIXS) with a sample with 10 % 57Fe isotopic enrichment (x = 1.4) and extensive DFT modeling (x = 1.5) we obtain the element and site-resolved phonon density of states in the ordered and the paramagnetic state. These allow us to understand the impact of magnetoelastic interactions on the vibrational entropy change at the magnetic phase transition.

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