Nonlinear magneto-optics in magnetic nanoparticles

In this paper, the results of our recent studies of the magnetization-induced nonlinear optical effects in magnetic nanoparticles are surveyed. There are three aspects of nonlinear magneto-optics of nanoparticles, which attract attention in this review being interdisciplinary in terms of magnetism, low-dimensionality, nonlinear and coherent optics. The first is the fact that the nonlinear magneto-optical Kerr effect (NOMOKE), i.e. magnetization-induced second-harmonic generation (MSHG), exists in magnetic nanogranular films simultaneously with giant magnetoresistance effect (GMR). Moreover, the NOMOKE contrast attains maximum at the same content of magnetic component in magnetic nanogranular films as the maximum of GMR coefficient. Up to now nonlinear magneto-optics was concentrated on the regular magnetic systems and as a consequence described a coherent nonlinear response. On the contrary, in recent studies an attention is turned to the random magnetic nanostructures and, in particular, to the random two-dimensional arrays of magnetic nanoparticles fabricated by Self-Assembly techniques. Thus, an incoherent analog of MSHG, which can be called: magnetization-induced hyper-Rayleigh scattering, is observed. And finally a general issue of intrinsic weakness of magnetization-induced nonlinear optical effects governed by the fine structure parameter is discussed in terms of internal homodyne effect as one of the mechanisms of an enhancement of the magnetic effects in nonlinear optics. (C) 2002 Elsevier Science B.V. All rights reserved.