Influence of hydrogenation on the vibrational density of states of magnetocaloric LaFe11.4Si1.6H1.6
New joint publication of UDE and TU Darmstadt teams
2020/02/18
Physical Review B 101 , 064415 (2020)
A. Terwey, M. E. Gruner, W. Keune, J. Landers, S. Salamon, B. Eggert, K. Ollefs, V. Brabänder, I. Radulov, K. Skokov, T. Faske, M. Y. Hu, J. Zhao, E. E. Alp, C. Giacobbe, O. Gutfleisch, H. Wende
In this work, performed in close cooperation with University of Duisburg-Essen, Advanced Photon Source (APS), Argonne National Laboratory and European Synchrotron Radiation Facility (ESRF), we studied the impact of magnetoelastic coupling on the magnetocaloric properties of LaFe11.4Si1.6H1.6 in terms of the vibrational (phonon) density of states (VDOS), which we determined with 57Fe nuclear resonantinelastic x-ray scattering (NRIXS) measurements and with density functional theory (DFT) based first-principles calculations in the ferromagnetic (FM) low-temperature and paramagnetic (PM) high-temperature phase. In experiments and calculations, we observe pronounced differences in the shape of the Fe-partial VDOS between nonhydrogenated and hydrogenated samples. This shows that hydrogen not only shifts the temperature of the first-order phase transition, but also affects the elastic response of the Fe subsystem significantly. In turn, the anomalous redshift of the Fe VDOS, observed by going to the low-volume PM phase, survives hydrogenation. Hydrogenation is observed to induce an overall blueshift of the Fe VDOS with respect to the H-free compound; this effect, together with the enhanced Debye temperature observed, is a fingerprint of the hardening of the Fe sublattice by hydrogen incorporation. In addition, the mean Debye velocity of sound of LaFe11.4Si1.6H1.6 was determined from the NRIXS and the DFT data.
