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 LaFe_13−xSi_x — •Markus Ernst Gruner^1,2, Werner Keune^2,3, Beatriz Roldan Cuenya⁴, Joachim Landers², Sergey Makarov², David Klar², Michael Y. Hu⁵, Ercan E. Alp⁵, Maria Krautz¹, Oliver Gutfleisch⁶, and Heiko Wende² — ¹IFW 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 LaFe_13−xSi_x, 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.