PERPENDICULAR ANISOTROPY DETECTED BY TRANSVERSELY BIASED INITIAL SUSCEPTIBILITY VIA THE MAGNETOOPTIC KERR-EFFECT IN FEXSI1-X THIN-FILMS ANDFEXSI1-X SI MULTILAYERS - THEORY AND EXPERIMENT/

We studied experimentally and theoretically the perpendicular anisotro py and the stripe-domain structure in both FexSi1-x thin films and Fex Si1-x/Si multilayers, the latter being in the low-modulation-length re gime (0.4 nm<lambda<7 nm). The experimental study was made by means of the transversely biased initial susceptibility chi(t beta) via the ma gneto-optic Kerr effect. The samples under study were prepared by de t riode sputtering at T-S = 300 K. It is found that the appearance of st ripe domains is more pronounced for decreasing lambda as x remains con stant and may be caused by both the increase in effective magnetic thi ckness and the reduction in effective magnetization as lambda decrease s. For multilayers with lambda = 0.4 nm, the observed field dependence of chi(t beta)(-1) is similiar to that found in homogeneons thin film s when weak stripe-domain structures arise as a consequence of the exi stence of perpendicular anisotropy K-N. We propose a quasistatic one-d imensional model to explain the behavior of chi(t beta)(-1) when strip e domains are present, and we analyze the critical occurrence of strip e domains. We calculated the so-called pseudo-uniaxial anisotropy fiel d H-Ks, associated with the stripes, in two extreme cases: exchange-dr iven susceptibility or magnetic free poles (nonzero divergence in the bulk). The latter case agrees better with experiment. We found that pe rpendicular anisotropy is nor exclusive of a well-defined multilayer s tructure; i.e., K-N arises even when there are no interfaces in the vo lume. By setting the experimental saturation field H-S (obtained by hy steresis loops) into our model, we obtain both the perpendicular aniso tropy constant K-N=10(4)-10(5) J/m(3) and the critical thickness t(c) for the occurrence of a stripe-domain structure. Some possible sources of perpendicular anisotropy are discussed, for example, the associate d isotropic compressive stress sigma, whose contribution is found to b e \K-N\(magnetoel)approximate to 1.5-4.5 x 10(4) J/m(3).