Strong magnetic linear dichroism in Fe L ₂₃ and O K electron energy-loss near-edge spectra of antiferromagnetic hematite α-Fe₂O₃

Abstract

We report strong magnetic linear dichroism (MLD) at the Fe L ₂₃ and O K edges of the antiferromagnetic compound hematite α-Fe₂ O₃ in high-resolution orientation- and temperature-dependent electron energy-loss spectroscopy (EELS). Large intensity differences of corresponding spectral features are observed when the Fe L ₂₃ and O K edges are measured with momentum transfer either parallel or perpendicular to the magnetization. The resultant difference spectra for the Fe L ₂₃ edges is consistent with the MLD observed in X-ray absorption spectroscopy. For the first time we have observed MLD at the O K edge, where the magnetic origin of this dichroism is demonstrated by temperature-dependent investigations across the Morin transition temperature T _M = 263 K, at which the Fe electron spins, i.e. the magnetic moments, rotate by 90°. The O K edge MLD is interpreted in terms of superexchange between the spins of the Fe 3d and O 2p electrons through overlapping Fe 3d and O 2p orbitals. The experiments were performed in a transmission electron microscope (TEM), yielding information about the anisotropic electronic structure at nanoscale spatial resolution when operated with a focused electron probe. The effects of MLD at the Fe L ₂₃ edges on the determination of Fe³⁺/ΣFe in hematite at submicrometre scale using different independent quantification methods are discussed.