Dresden 2017 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 10: Caloric Effects in Ferromagnetic Materials

MA 10.12: Vortrag

Montag, 20. März 2017, 18:15–18:30, HSZ 04

Vibrational density of states in magnetocaloric, hydrogenated La(FeSi)₁₃-based compounds — •Alexandra Terwey¹, Joachim Landers¹, Soma Salamon¹, Werner Keune¹, Valentin Brabänder², Oliver Gutfleisch², Michael Y. Hu³, Jiyong Zhao³, E. Ercan Alp³, Markus E. Gruner¹, and Heiko Wende¹ — ¹Faculty of Physics and CENIDE, University of Duisburg-Essen, Germany — ²TU Darmstadt, Germany — ³APS, Argonne National Laboratory, USA

By employing ⁵⁷Fe nuclear resonant inelastic X-ray scattering as in [1], we determined the Fe-projected vibrational density of states (VDOS) of hydrogenated LaFe_11.4Si_1.6H_y and non-hydrogenated Mn-doped La_1.06Fe_11.4Si_1.5Mn_0.1 as well as hydrogenated and Mn doped La_1.06Fe_11.4Si_1.5Mn_0.1H_y. The hydrogenated compounds have potential use as refrigerants due to a first-order magneto-structural phase transition near room temperature. Distinct differences between the VDOS of non-hydrogenated and hydrogenated samples were discovered. This finding is in qualitative agreement with preliminary results from DFT calculations. Vibrational thermodynamic quantities were calculated from the VDOS. The change of vibrational entropy and specific heat across the phase transition was found to be smaller for the hydrogenated than for the non-hydrogenated samples. Our results demonstrate that knowledge of the VDOS is important to understand intrinsic thermodynamics of these magnetocaloric materials. Funding by the DFG (SPP1599) and U.S. DOE (DE-AC02-06CH11357) is acknowledged. [1] M.E. Gruner et al., Phys.Rev.Lett. 114, 057202 (2015)