Perpendicular and in-plane hole asymmetry in a strained NiFe₂O₄film

Strained materials can exhibit drastically modified physical properties in comparison to their fully relaxed analogues. We report on the x-ray absorption spectra (XAS) and magnetic circular dichroism (XMCD) of a strained NiFe₂O₄inverse spinel film grown on a symmetry matched single crystal MgGa₂O₄substrate. The Ni XAS spectra exhibit a sizable difference in the white line intensity for measurements with the x-ray electric field parallel to the film plane (normal incidence) vs when the electric field is at an angle (off-normal). A considerable difference is also observed in the FeL_2,3XMCD spectrum. Modeling of the XAS and XMCD spectra indicate that the modified energy ordering of the cation 3dstates in the strained film leads to a preferential filling of 3dstates with out-of-plane character. In addition, the results point to the utility of x-ray spectroscopy in identifying orbital populations even with elliptically polarized x-rays.