Berlin 2018 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 7: Focus Session: Magnetism in Materials Science: Thermodynamics, Kinetics and Defects I (joint session MM/MA)
MA 7.6: 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.