Perpendicular and in-plane hole asymmetry in a strained NiFe₂O₄ film

Abstract

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 NiFe2O4 inverse spinel film grown on a symmetry matched single crystal MgGa2O4 substrate. 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 Fe L 2,3 XMCD spectrum. Modeling of the XAS and XMCD spectra indicate that the modified energy ordering of the cation 3d states in the strained film leads to a preferential filling of 3d states 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.

Near-surface electronic structure in strained Ni-ferrite films: An x-ray absorption spectroscopy study

“…However, in the dichroism spectrum, the B peak is generally higher in intensity than the A peak. In general, we conclude that the overall shape of the Ni 2þ XMCD spectra is consistent with earlier reports for NiFe 2 O 4 , [46][47][48] and to a first approximation the spectra are insensitive to the lattice mismatch of the NiFe 2 O 4 with the substrate. However, the integrated intensity distribution between the L 3 and L 2 edges displays subtle shifts, as discussed below.…”

“…In some cases, the weaker peak at 707 eV appears as more of a shoulder on the main L 3 feature. In prior reports, 46 this weaker feature has been associated with a small contribution from Fe 2þ cations which may be introduced in the sample via oxygen vacancies and other defects. As is the case with the Ni spectra, the Fe L 2 features are comprised of two primary features.…”

“…The Ni XAS and XMCD spectra are consistent for all the samples and also with previously published Ni-spectra for ferrites. [46][47][48] For NFO∖∖MGO, only in-plane spectra were acquired.…”

“…3(b)], which was also previously observed for other spinel ferrites. 23,46,50 The lowest energy negative feature I is most likely a contribution from a small amount of Fe 2þ originating from defect states. 51 XMCD spectral features II and III are associated with Fe 3þ cations on T d and O h sites, respectively.…”

Optical and extreme UV studies of spin dynamics in metallic and insulating ferrimagnets

“…Ni-ferrite (NiFe 2 O 4 ) has an inverse spinel structure [32], where the octahedral sites (O h or in the bulk as a fully inverse spinel with a cubic lattice parameter of a = 0.8345 nm. In this section we will focus on exploring the element-specific spin-dynamics at ultrafast timescale, in the particular example of a strained, insulating ferrimagnetic thin film.…”