Effects of Magnetic Ordering on Hole Polaron Transport in Hematite: The Critical Role of Superexchange Interactions

Within the class of technologically important transition metal oxide quantum materials, strong electronic correlations in magnetic oxide semiconductors arise from partially filled d shells. For magnetic oxide semiconductors, superexchange interactions fundamentally determine the magnetic ordering and can greatly affect the electronic structures and physical properties. The formation of self-trapped small hole polarons is known to hinder the transport properties and, thus, the device applications. Many strategies (e.g., temperature, doping, etc.) have been proposed to enhance hole polaron transport in magnetic oxide semiconductors. However, the slow mobilities of the hole polarons continue to limit the device performance. As a potential alternative approach, the feasibility of magnetic-field control and how the effect of superexchange interactions on the transport properties of small hole polarons remains to be clarified. In the prototypical magnetic oxide semiconductor α-Fe₂O₃, we computationally studied the superexchange interactions, p-d hybridizations, formation energies, and hopping barriers of hole polarons. Two types of magnetic ordering are contrasted: antiferromagnetic and ferromagnetic. We found that ferromagnetic ordering leads to higher formation energy, smaller diffusion barrier, and isotropic diffusion of the hole polaron due to the weakened superexchange strength. This comparative study provides insights into the interplay between exchange interactions and hole polaron transport and demonstrates the capability for enhancing the transport properties of small hole polarons in magnetic oxide semiconductors through magnetic-field control.