Publications in Scientific Journals:

M. Wolloch, M. Gruner, W. Keune, P. Mohn, J. Redinger, F. Hofer, D. Suess, R. Podloucky, J. Landers, S. Salamon, F. Scheibel, D. Spoddig, R. Witte, B. Roldan Cuenya, O. Gutfleisch, M. Hu, J. Zhao, T. Toellner, E. Alp, M. Siewert, P. Entel, R. Pentcheva, H. Wende:
"Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin Films";
Physical Review B, 94 (2016), 1744351 - 17443517.

English abstract:
We present phonon dispersions, element-resolved vibrational density of states (VDOS) and corresponding
thermodynamic properties obtained by a combination of density functional theory (DFT) and nuclear resonant
inelastic x-ray scattering (NRIXS) across the metamagnetic transition of B2 FeRh in the bulk material and thin
epitaxial films. We see distinct differences in the VDOS of the antiferromagnetic (AF) and ferromagnetic (FM)
phases, which provide a microscopic proof of strong spin-phonon coupling in FeRh. The FM VDOS exhibits a
particular sensitivity to the slight tetragonal distortions present in epitaxial films, which is not encountered in
the AF phase. This results in a notable change in lattice entropy, which is important for the comparison between
thin film and bulk results. Our calculations confirm the recently reported lattice instability in the AF phase.
The imaginary frequencies at the
point depend critically on the Fe magnetic moment and atomic volume.
Analyzing these nonvibrational modes leads to the discovery of a stable monoclinic ground-state structure, which
is robustly predicted from DFT but not verified in our thin film experiments. Specific heat, entropy, and free
energy calculated within the quasiharmonic approximation suggest that the new phase is possibly suppressed
because of its relatively smaller lattice entropy. In the bulk phase, lattice vibrations contribute with the same sign
and in similar magnitude to the isostructural AF-FM phase transition as excitations of the electronic and magnetic
subsystems demonstrating that lattice degrees of freedom need to be included in thermodynamic modeling.

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