Electronic and Optical Properties of a Semiconducting Spinel (Fe2CrO4)

Epitaxial chromium ferrite (Fe 2 CrO 4 ), prepared by state‐of‐the‐art oxygen plasma assisted molecular beam epitaxy, is shown to exhibit unusual electronic transport properties driven by the crystallographic structure and composition of the material. Replacing 1/3 of the Fe cations with Cr converts the host ferrimagnet from a metal into a semiconductor by virtue of its fixed valence (3+); Cr substitutes for Fe at B sites in the spinel lattice. By contrast, replacing 2/3 of the Fe cations with Cr results in an insulator. Three candidate conductive paths, all involving electron hopping between Fe 2+ and Fe 3+ , are identified in Fe 2 CrO 4 . Moreover, Fe 2 CrO 4 is shown to be photoconductive across the visible portion of the electromagnetic spectrum. As a result, this material is of potential interest for important photo‐electrochemical processes such as water splitting.