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Berlin 2018 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 5: Topical session (Symposium EPS and MM, joint session with MA): Magnetism in Materials Science: Thermodynamics, Kinetics and Defects (joint session MM/MA)

MM 5.6: Topical Talk

Montag, 12. März 2018, 12:15–12:45, TC 010

Interplay of moment-volume and electron-phonon coupling in the itinerant electron metamagnet LaFe13−xSixHy — •Markus Ernst Gruner — Faculty of Physics and Center for Nanointegration, CENIDE, University of Duisburg-Essen, Germany

LaFe13−xSixHy compounds belong to the most promising systems for room temperature magnetic refrigeration. Here, large adiabatic temperature and isothermal entropy changes in an external magnetic field are obtained at a first-order metamagnetic transition. It is accompanied by a large volume change without change in lattice symmetry, attributed to the competition of different magnetic states of Fe associated with varying atomic volumes. Recently, we detected by first-principles lattice dynamics and nuclear resonant inelastic X-ray scattering characteristic changes in the vibrational density of states at the magnetic transition in LaFe13−xSix, which involves the disappearance of a high-energy peak in connection with an overall softening of phonons in the paramagnetic phase. This contributes to the good magneto- and barocaloric properties of the material, in terms of a cooperative contribution of magnetic, electronic and vibrational degrees of freedom to the entropy change. The softening originates from adiabatic electron-phonon coupling caused by specific changes in the electronic density of states at the Fermi level, which are sensitive to the magnitude of the Fe moment, rather than to magnetic order. Finally, we demonstrate that the same mechanisms are effective in the hydrogenated compound at ambient conditions.
Funding by the DFG within SPP 1599 is gratefully acknowledged.

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