Nonlinear Magneto-Optical Kerr Effect in Gd-Containing Langmuir-Blodgett Films
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EXPERIMENT The organo-metallic LB films are prepared by the Langmuir-Blodgett technique on fused quartz substrates from a solution of stearic acid in chloroform spread on the water subphase. Gd3 ions ÷ are dissolved in water from Gd acetate of 5x 10-4 M concentration and are adsorbed at the floating stearic acid monolayer. This allows for the creation of twodimensional areas of magnetic ions binded to the solid organic monolayers. The structural unit of periodic LB film 5 nm thick consists of the monolayer of Gd 31 ions surrounded by two monolayers of stearic acid. The films composed of 40 structural units are studied. The area per Gd ion in the monolayer is -10 A42 and the distance between Gd 31 ions in monolayer is about 3.3 A. SHG from the quartz substrate and the LB films of pure stearic acid are found to be negligibly small as compared with the SHG signal from the Gd containing LB films. The NOMOKE is studied for the longitudinal magnetization of the film. The output of a Q-switched YAG:Nd 3 laser ÷ at the wavelength of 1064 nm, a pulse duration of 15 ns and a repetition rate of 12.5 Hz is used as a fundamental radiation. The SHG signal generated from LB film is selected by bandpass filters and detected by a PMT and gated electronics. The fundamental pulse intensity is about 1 MW/cm 2 for the laser spot diameter of about I mm. The magneto-induced phase shift of the SH wave, i.e. SHG magnetoinduced 40 o0 interferometry [9], is studied 35 by the use of a thin Sn0 2 as the sourse of a reference SH 30 wave. The phase shift between a 25,, the SH waves generated by the sample and by the reference is 20 V, ,, varied as the distance d between the reference and the is sample is changed [10]. ',120 10 o - 1ke Azimuthal angular S}..__ + 1 k~e] cj anisotropy of the SHG 5 intensity testifies that the films 60 120 ISO 00 240 300 36 are isotropic. Analyzer angle (deg.) Magnetoinduced changes in Figure 1. SHG polarization diagrams for Gd-LB the SH response from Gdfilms measured for the longitudinal NOMOKE; containing LB films are studied the fundamental radiation is s-polarized, (p=O by measuring the SH wave corresponds to the p-polarized SHG. i.e. polarisation diagrams, dependences of the SHG intensity on the rotation angle of the analyzer (p, for the geometry of the longitudinal NOMOKE. The magnetoinduced rotation of the SHG polarisation, measured for the saturating magnetic fields of the opposite signes and for the s-polarised fundamental radiation, is found to be about 120 (Fig. 1). The MSHG interferometry pattern for the longitudinal NOMOKE measured in s-in, sout geometry indicates the 1300 shift of the phase of the SH wave for the opposite directions of magnetic fields ±1 kOe (Figure 2, a). For the p-in, p-out SHG the similar dependences reveal no differences within the experimental accuracy (Figure 2, b). 658
DISCUSSION Consider first the polarisation of the SHG radiation reflected from GdLB films. It can be seen from both the NOMOKE and SHG interferometry experiments that the sin, s-out SHG response exists. It is we
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