Scaling of quadratic and linear magneto-optic Kerr effect spectra with L2₁ordering of Co₂MnSi Heusler compound

Spectral ellipsometry is a useful technique allowing fast, nondestructive, and contactless characterization of thin films and constituent materials. In this Letter, we show that both the linear magneto-optic Kerr effect (LinMOKE, proportional to the magnetization M) and the quadratic MOKE (QMOKE, proportional to M 2) can be a useful extension of spectral ellipsometry and are able to sense the crystallographic ordering of Heusler compounds. This is demonstrated for the Heusler compound Co2MnSi, which has a crystallographic transition from a B2 to an L21 structure with increasing annealing temperature Ta. We investigated a set of Co2MnSi thin films deposited on MgO(001) substrates and annealed from 300 to 500 °C. The amplitude of LinMOKE and QMOKE spectra, detected in the extended visible spectral range of 0.8-5.5 eV, scales linearly with Ta, and this effect is pronounced at the resonant peaks of the QMOKE spectra below 2.0 eV. Furthermore, the spectra of the magneto-optic (MO) parameters, which fully describe the MO response of Co2MnSi up to the second order in M, are obtained depending on Ta. Finally, the spectra are compared with ab initio calculations of a purely L21-ordered Co2MnSi Heusler compound.