Raman study of the Verwey transition in magnetite thin films

Abstract

We have grown epitaxial thin films of magnetite on MgO and Al _2 O _3 substrates with sharp and distinct signatures of the Verwey transition in resistivity and magnetization. We have used Raman scattering to separate the footprint of purely structural changes from the effect of additional charge and orbital order. Raman modes related to the structural phase transition occur first at temperatures above the Verwey transition temperature. In contrast, newly emerging modes indicating additional charge and orbital order appear at the Verwey transition. These results suggest that the completion of the structural phase transition in magnetite is a necessary precursor triggering a transition into a complex charge and orbitally ordered state.