Speaker
Description
Magnetite is the first discovered magnetic material. At $T$=125~K, the Verwey phase transition is observed, in which the electric conductivity decreases by two orders of magnitude [1]. At room temperature, magnetite crystallizes in an inverse spinel structure, in which tetrahedrally coordinated A-sites are occupied by Fe$^{3+}$ ions, while octahedrally coordinated B-sites are occupied by randomly distributed Fe$^{3+}$ and Fe$^{2+}$ ions. At the Verwey temperature, magnetite exhibits the structural phase transition from the cubic to monoclinic phase with the charge-orbital order [2].
Using the density functional theory, we studied the lattice dynamical properties of magnetite in the cubic symmetry [3]. We found a strong electron-phonon coupling, which plays the important role in the Verwey transition. The anomalous phonon broadening resulting from this interaction was observed by the inelastic X-ray scattering studies [4]. The discrepancy between the calculated and measured phonon density of states (DOS) indicates the existence of short-range order with local deformations in the cubic phase. In contrast, the phonon DOS obtained for the monoclinic structure shows a very good agreement with the nuclear inelastic scattering [5]. The interplay between the structural and dynamical properties of magnetite was demonstrated by the recent pump-probe experiments [6], which revealed new features of the collective modes.
This work was partially supported by National Science Centre (NCN, Poland) under grant UMO-2017/25/B/ST3/02586.
Refs
[1] E. J. W. Verwey, Nature {\bf 144}, 327 (1939).
[2] M. S. Senn, J. P. Wright and J. P. Attfield, Nature {\bf 481}, 173 (2012).
[3] P. Piekarz, K. Parlinski and A. M. Oleś, Phys. Rev. Lett. {\bf 97}, 156402 (2006).
[4] M. Hoesch, P. Piekarz, A. Bosak, M. Le Tacon, M. Krisch, A. Kozłowski, A. M. Oleś and K. Parlinski, Phys. Rev. Lett. {\bf 110}, 207204 (2013).
[5] T. Kołodziej, A. Kozłowski, P. Piekarz, W. Tabiś, Z. Kąkol, M. Zając, Z. Tarnawski, J. M. Honig, A. M. Oleś and K. Parlinski, Phys. Rev. B {\bf 85}, 104301 (2012).
[6] S. Borroni, E. Baldini, V. M. Katukuri, A. Mann, K. Parlinski, D. Legut, C. Arrell, F. van Mourik, J. Teyssier, A. Kozłowski, P. Piekarz, O. V. Yazyev, A. M. Oleś, J. Lorenzana and F. Carbone, Phys. Rev. B {\bf 96}, 104308 (2017).
