Magneto-optical effects in second harmonic generation from W/Co/Pt nanofilms

Abstract

Interfaces between ferromagnetic metals and nonmagnetic specimen attract much attention as they are very important for the formation of magnetic properties of nanostructures. Vice versa, specific magnetic ordering at such interfaces may provide new effects in their optical and nonlinear optical response. In this work we study the magnetization-induced effects in optical second harmonic generation (SHG) in W/Co/Pt-based thin films with the thicknesses of the Co layer of 2 – 10 nm. Besides common odd in magnetization effects in the SHG intensity, we observe additional one that is not expected for homogeneously magnetized ferromagnetic films, which consists in modulation of p-polarized SHG intensity under longitudinal magnetic field application. The phenomenological description of the observed effect is performed in terms of gradient and second-order in magnetization contributions to the SHG polarization, where gradient of magnetization along the normal to the structure plays the key role.

Nonlinear Optical Microscopy of Interface Layers of Epitaxial Garnet Films

“…It is also known for its high surface sensitivity if being applied to materials with intrinsic inversion symmetry [26][27][28][29][30]. In the case of iron garnet films, the application of the SHG technique is beneficial due to (i) symmetry forbiddance of the even-order nonlinear optical effects (including SHG) in the bulk of centrosymmetric materials such as yttrium iron garnet crystals (in the electric dipole approximation), which provides high SHG sensitivity to the properties of the interface regions with inevitably broken inversion symmetry [23,31,32], (ii) absence of the SHG contribution from the substrates, which is typically centrosymmetric gallium-gadolinium garnet (GGG) of a few hundreds of microns in thickness and which can also reveal weak MO responses, (iii) the large value of the MO effects in the SHG response and (iv) larger (as compared to the linear MO microscopy) SHG spatial resolution originating from the nonlinear nature of the effect, and (v) the ability to use a multiple-color pump and probe experimental schemes. As an example, magnetic domains were visualized via the SHG microscopy in [33] in the scheme of the magnetooptical Faraday effect in iron garnet films of different crystallographic orientations, which provided additional information on the domain's magnetization distribution as compared to a linear magnetooptical probe.…”