TBIS measurements performed by MOKE for the study of soft ferromagnetic thin films and sandwiches: In-plane and biaxial anisotropies, local anisotropy and dispersion

Magneto-optic effects have been proved to be a premier tool for the study of magnetic thin films. In the case of films thinner than 1000 Angstrom and if there is no appreciable variation of the magnetic structure through the thickness, the magneto-optic effects provide complete information, It is noteworthy that transverse biased initial susceptibility (TBIS) measurement is very sensitive, for it allows a precise determination of the anisotropy field and, moreover, to quantify the the origin of which is different. If the samples are deposited on glass substrates, by performing TBIS measurements with a magneto-optic transverse Kerr effect (MOKE) we can obtain information of the processes occurring at both film/air and glass/film interfaces, providing information of the variation of the magnetic properties through the thickness. We have successfully applied this technique for the study of thin films and sandwiches, focusing our attention on the following items: (1) Uniaxial in-plane anisotropy, local anisotropy and anisotropy dispersion in transition metal-rare-earth thin films, We have investigated the dependence of the uniaxial anisotropy and its dispersion on the rare-earth substituted and on the composition. Using the ripple theory we have evaluated the local anisotropy as a function of the rare-earth content, and we have found a very nice correlation between macroscopic and local anisotropies, allowing us to establish the origin of the macroscopic anisotropy in these alloys. (2) TBIS measurements can also be used 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 perpendicular 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 are not magnetically homogeneous, they may present different magnetic phases which may be made evident by our technique. (4) We recently extended this technique to the study of ferromagnetic double-layered and sandwiched films. In these systems the magnetic and magneto-optical properties are strongly influenced by the coupling at the interfaces. The high sensitivity of our procedure allowed us to distinguish between two contributions to the anisotropy dispersion in sandwiched films: a well-known term due to the in-plane anisotropy skew (long-range fluctuations of the in-plane easy axis) and a contribution due to the existence of a weak perpendicular anisotropy.