TBIS MEASUREMENTS PERFORMED BY MOKE FOR THE STUDY OF SOFT FERROMAGNETIC THIN-FILMS AND SANDWICHES - INPLANE AND BIAXIAL ANISOTROPIES, LOCALANISOTROPY AND DISPERSION

Magneto-optic effects have been proved to be a premier tool for the st udy of magnetic thin films. In the case of films thinner than 1000 Ang strom and if there is no appreciable variation of the magnetic structu re through the thickness, the magneto-optic effects provide complete i nformation, It is noteworthy that transverse biased initial susceptibi lity (TBIS) measurement is very sensitive, for it allows a precise det ermination of the anisotropy field and, moreover, to quantify the the origin of which is different. If the samples are deposited on glass su bstrates, by performing TBIS measurements with a magneto-optic transve rse Kerr effect (MOKE) we can obtain information of the processes occu rring at both film/air and glass/film interfaces, providing informatio n of the variation of the magnetic properties through the thickness. W e have successfully applied this technique for the study of thin films and sandwiches, focusing our attention on the following items: (1) Un iaxial in-plane anisotropy, local anisotropy and anisotropy dispersion in transition metal-rare-earth thin films, We have investigated the d ependence of the uniaxial anisotropy and its dispersion on the rare-ea rth substituted and on the composition. Using the ripple theory we hav e evaluated the local anisotropy as a function of the rare-earth conte nt, and we have found a very nice correlation between macroscopic and local anisotropies, allowing us to establish the origin of the macrosc opic anisotropy in these alloys. (2) TBIS measurements can also be use d as an alternative technique to measure perpendicular anisotropy, We have developed a theoretical model to explain the particular behaviour of TBIS curves in the most general case when both in-plane and perpen dicular anisotropies are present (biaxial anisotropy). From the fit of the experimental curves to the theoretical model we can obtain the in -plane and the perpendicular anisotropy fields. (3) When the samples a re not magnetically homogeneous, they may present different magnetic p hases which may be made evident by our technique. (4) We recently exte nded this technique to the study of ferromagnetic double-layered and s andwiched films. In these systems the magnetic and magneto-optical pro perties are strongly influenced by the coupling at the interfaces. The high sensitivity of our procedure allowed us to distinguish between t wo contributions to the anisotropy dispersion in sandwiched films: a w ell-known term due to the in-plane anisotropy skew (long-range fluctua tions of the in-plane easy axis) and a contribution due to the existen ce of a weak perpendicular anisotropy.