Magnetization - induced optical third - harmonic generation in Co and Fe nanostructures

Magnetization-induced optical third-harmonic generation (MTHG) is observed in magnetic nanos-tructures: Co and F e nanolayers and granular films containing Co nanoparticles. Magnetization-induced variations of the MTHG characteristics in these nanostructures exceed the typical values of linear magneto-optical Kerr effect by at least an order of magnitude: the maximum of magnetic contrast in the MTHG intensity is up to 0.2, the angle of polarization rotation for MTHG is 10 • and the relative phase shift is up to 100 •. Magneto-optics, with its more than century-long history , remains one of the most important experimental methods in studies of magnetism. Recently, significant attention has been directed towards nonlinear magneto-optics [1]: nonlinear magneto-optical Faraday and Kerr effects in second-harmonic generation (SHG) were observed experimentally in yttrium-iron-garnet films [2], then at surfaces of magnetic metals [3], in magnetic mul-tilayers [4] and nanogranules [5]. Experimental measurements [2-5] and theoretical estimates [6] reveal the typical magnitudes of the magnetization-induced effects in SHG: the magnetization-induced variations of the SHG intensity and rotation of the second-harmonic (SH) wave polarization, may exceed the linear magneto-optical Kerr effect (MOKE) by orders of magnitude. It is well recognized that magnetization-induced SHG (MSHG) is a powerful probe of surface and interface magnetism [1,6,7]. The latter comes about from the lack of dipole magnetization-induced second-order susceptibility in the bulk of centrosymmetric magnetic materials. In contrast to the bulk, the surface of centrosymmetric materials is always noncentrosymmetric and results in local-ization of the dipole magnetization-induced nonlinear polarization at the surface. MSHG comes from the surface layer that is several nanometers thick and probes the surface magnetic properties. Meanwhile, this high surface sensitivity of MSHG is extruded in shadow third-order nonlinear magneto-optical effects because of their bulk localization as well as their small expected value. This is why the observation of magnetization-induced third-harmonic generation (MTHG) is discussed just recently in garnet films [8,9] and magnetic alloys [10]. On the other hand, both the surface MSHG and bulk MTHG are expected to supplement each other as magneto-optical probes and provide complementary information about the magnetic properties of nanostructures. In this paper, magnetization-induced THG is observed in the following magnetic nanostructures: Co and F e nanolayers, and granular films containing Co nanoparti-cles. For the description of MTHG, one can follow the phenomenological approach which has been developed for the MSHG effects [1]. According to this approach, the third-order susceptibility of a magnetic material is a combination …