Quadratic magneto-optic Kerr effect spectroscopy of Fe epitaxial films on MgO(001) substrates

Abstract

The magneto-optic Kerr effect (MOKE) is a well known and handy tool to characterize ferro-, ferri-, and antiferromagnetic materials. Many of the MOKE techniques employ effects solely linear in magnetization M. Nevertheless, a higher-order term being proportional to M-2 and called quadratic MOKE (QMOKE) can additionally contribute to the experimental data. Here, we present detailed QMOKE spectroscopy measurements in the range of 0.8-5.5 eV based on a modified eight-directional method applied on ferromagnetic bcc Fe thin films grown on MgO substrates. From the measured QMOKE spectra, two further complex spectra of the QMOKE parameters G(s) and 2G(44) are yielded. The difference between those two parameters, known as Delta G, denotes the strength of the QMOKE anisotropy. Those QMOKE parameters give rise to the QMOKE tensor G, fully describing the perturbation of the permittivity tensor in the second order in M for cubic crystal structures. We further present experimental measurements of ellipsometry and linear MOKE spectra, wherefrom permittivity in the zeroth and the first order in M are obtained, respectively. Finally, all those spectra are described by ab initio calculations.