Theory of Nonlinear Magneto-Optics

TL;DR

This paper theoretically analyzes the nonlinear magneto-optical Kerr effect in ferromagnetic thin films, demonstrating how electronic properties influence spectra and how nonlinear effects enhance sensitivity to magnetic and structural features.

Contribution

It introduces a theoretical framework for interpreting nonlinear Kerr spectra to extract electronic and magnetic properties of ferromagnetic thin films and interfaces.

Findings

Nonlinear Kerr spectra can reveal electronic band width, magnetization, and film thickness.

Second harmonic Kerr rotation is 10-100 times larger than linear Kerr rotation.

Symmetry considerations allow determination of magnetization direction from nonlinear spectra.

Abstract

Nonlinear magneto-optics is a very sensitive fingerprint of the electronic, magnetic, and atomic structure of surfaces, interfaces, and thin ferromagnetic films. Analyzing theoretically the nonlinear magneto-optical Kerr effect for thin films of Fe(001) and at Fe surfaces we demonstrate exemplarily how various electronic material properties of ferromagnets , such as the $d$-band width, the magnetization, the substrate lattice constant, and the film-thickness dependence can be extracted from the calculated nonlinear Kerr spectra. Furthermore, we show how the substrate $d$ electrons (Cu(001)) affect the nonlinear Kerr spectra even without being themselves spin-polarized and without film-substrate hybridization. We show that the Kerr rotation angle in second harmonic generation is enhanced by one to two orders of magnitude compared to the linear Kerr angle and how symmetry can be used to obtain the direction of magnetization in thin films and at buried interfaces from nonlinear magneto-optics.