Magnetic Second Harmonic Generation Studies of Co-Cu Granular Films
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shows the STM pattern for such a film. To study the nonlinear-optical properties of Co-Cu granular films the azimuthal anisotropy of the
k
IILSA V. 1424A Zi
SHG intensity is studied using the output of a Qswitched YAG:Nd÷3 laser at a wavelength of 1064 nm, with a pulse duration of 15 ns and an intensity of 2 MW/cm 2 . In the NOMOKE studies a DC-magnetic field up to 1 kOe is applied. The longitudinal NOMOKE is studied and compared with
the
M7.6A
Fig. 1. The STM pattern for the Co 0.42Cu0 .58 granular film.
results
of
spectroscopic studies.
the
MOKE
RESULTS Figure 2 shows the azimuthal dependence of the SHG 60 • p-in, s-out intensity from the Co0.42CuO.,5 film for A s-in, s-out o)W three combinations of polarization of • 50 p-in, p-ot the fundamental and second harmonic 0 (SH) wave. The clear two-fold and 40 four-fold symmetry is found for the s-in, '0 .- 30 s-out and p-in, s-out combinations, respectively. The four-fold symmetry combined with a strong one-fold pattern - 20 is observed for p-in, p-out combination. "A Figure 3 shows the dependence • 10 Vof the SHG intensity on the analyzer c, ' rotation angle in the Co0.42 CuO. 58 film for 0 two opposite directions of the magnetic 0 60 120 180 240 300 360 field applied in the transversal Azimuthal angle (deg) geometry. NOMOKE is characterized quantitatively by the magnetic contrast Fig.2. The azimuthal angular dependence p2.=(Im÷(20•)-Im.(2(o))/(Im+(20o)+Im, of the SHG intensity from the CoCu film. 2 (2c)), where IM+&.( co) is the MSHG intensity for opposite directions of the magnetization M The magnetic contrast P2. measured at a 50' angle of incidence is about 4x 10-2, while the linear MOKE contrast measured at the wavelengths 532 nm 1064 nm is about 10"3. Thus, NOMOKE exceed the linear analog by more than an order of magnitude. angular
A
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The magneto-induced phase shift of the SH wave [9] is in granular films with a thin Sn0 2 film 100 '80 (9 as a reference. Figure 4 shows the 80 1 0o 80 dependence of the MSHG intensity on the reference position (the SHG " 60, interference pattern) for the ' Co0 .42Cuo.58 film. The contrast of .the SHG interference pattern 40 depends on a coherence of the SH .0 o wave generated from the array of 0 20 the Co nanocrystals and on a o mutual coherence of the nonmagnetic and magnetic 00 60 120 180 240 300 360 contributions to the total SH field. Analyzer rotation angle (deg.) The magneto-induced shift of the interference pattern is about 0.5 cm Fig.3. The longitudinal NOMOKE. which corresponds to - 80 in the phase shift domain. The analysis of the MSHG data allows to consider the enhancement of the magnetoinduced effects in terms of the phenomenological models of the MSHG discussed in [6,7]. According to [6], the odd in magnetization M surface-bulk cross-terms (X( 2)Bx( 2)SAM) and (X(2)sX( 2)BMM) should enhance the appearance of magneto-induced alterations in the SHG intensity from noncentrosymmetric magnetic films due to the interference of the SH fields originating from the nonmagnetic bulk and surface dipole contr
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