Nonlinear magneto-optics of nanogranular films
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J6.7.1
Nonlinear magneto-optics of nanogranular films Evgenia M. Kim1, Tatyana V Murzina1, Oleg A Aktsipetrov1 and Anatolii F. Kravets2; 1 Department of Physics, Moscow State University, Moscow, Russia; 2 Institute of Magnetism, National Academy of Sciences of Ukraine, Kiev, Ukraine ABSTRACT In this paper, the results of experimental studies of magnetization-induced second- and third-order nonlinear optical effects in magnetic nanogranular films are described. Magnetization-induced variations of the intensity, polarization state and the phase of the harmonics’ waves are observed in magnetic nanogranular films of the composition CoxAg1-x and Cox(Al2O3)1-x. Nonlinear magneto-optical Kerr effect (NOMOKE) in third-harmonic generation is observed in these nanomaterials. The second- and third-order NOMOKE from granular films is shown to exceed the linear magneto-optical Kerr effect by at least an order of magnitude. INTRODUCTION Optical second-harmonic generation (SHG) is one of the most intensively studied phenomena in nonlinear optics of nano- and microstructures for the last two decades [1,2]. High interest in SHG is related to its unique sensitivity to structural, electronic, magnetic, ferroelectrics, etc. properties of surfaces, interfaces and low-dimensional structures. This sensitivity of the SHG probe is the result of the prohibition of the dipole-like quadratic susceptibility in the bulk of centrosymmetric materials, which restricts the existence of SHG at interfaces and in nanostructures [3]. For the case of magnetic low-dimensional structures, the combination of the breaking of the space symmetry and magnetization-induced breaking of the time-reversal symmetry results in the appearance of magnetization-induced effects in second-harmonic response [4]. As the magnetization does not break the inversion symmetry, the sources of magnetization-induced SHG (MSHG) are localized at surfaces and in nanostructures, which makes MSHG a sensitive probe of nanostructures’ magnetism [5,6]. This pronounced surface sensitivity of the MSHG probe kept for a long time in shadow magnetization-induced effects in third-order nonlinearoptical phenomena, as the bulk localization of the third-harmonic generation (THG) did not allow to expect large values of the magnetization-induced effects. However, third-harmonic generation and magnetization-induced THG (MTHG), seem to be very promising for probing magnetism and electronic properties in nanostructures. In this paper, the results of the experimental studies of magnetization-induced secondand third-order nonlinear optical effects in magnetic nanogranular films are discussed. EXPERIMENTAL DETAILS The studied samples are CoxAg1-x and Cox(Al2O3)1-x granular films of the composition 6 < x < 80 vol.% and of about 400 nm thick, deposited on glass ceramic substrates at room temperature at the residual pressure 10-4 Pa using dual electron beam deposition system as described elsewhere [8]. The crystalline structure of the films is studied by X-ray diffraction technique and reveals the existence
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