Jahn-Teller distortion driven magnetic polarons in magnetite

H. Y. Huang; Z. Y. Chen; R. -P. Wang; F. M. F. de Groot; W. B. Wu; J. Okamoto; A. Chainani; J. -S. Zhou; H. -T. Jeng; G. Y. Guo; Je-Geun Park; L. H. Tjeng; C. T. Chen; D. J. Huang

doi:10.1038/ncomms15929

paper

Jahn-Teller distortion driven magnetic polarons in magnetite

arXiv:1512.07957 · doi:10.1038/ncomms15929

Abstract

The first known magnetic mineral, magnetite (Fe $_{3}$ O $_{4}$ ), has unusual properties which have fascinated mankind for centuries; it undergoes the Verwey transition at $T_{V}$ $\sim$ 120 K with an abrupt change in structure and electrical conductivity. The mechanism of the Verwey transition however remains contentious. Here we use resonant inelastic X-ray scattering (RIXS) over a wide temperature range across the Verwey transition to identify and separate out the magnetic excitations derived from nominal Fe $^{2 +}$ and Fe $^{3 +}$ states. Comparison of the RIXS results with crystal-field multiplet calculations shows that the spin-orbital $dd$ excitons of the Fe $^{2 +}$ sites arise from a tetragonal Jahn-Teller active polaronic distortion of the Fe $^{2 +}$ O $_{6}$ octahedra. These low-energy excitations, which get weakened for temperatures above 350 K but persist at least up to 550 K, are distinct from optical excitations and best explained as magnetic polarons.