En las fronteras de la Materia Condensada

The exchange coupling between ferromagnetic layers in metallic multilayers has been a subject of intense research in the past ten years. The origin and characteristics of the interlayer coupling have been discussed in a lot of theoretical and experimental articles, but up to now, they are still open questions. Moreover, structures involving ferromagnetic layers separated by non-magnetic insulators or semiconductors are presently investigated in order to optimize magnetoresistive properties of tunnel junctions. Recent articles show that the tunnel magnetoresistance (TMR) not only depends on the electrodes spin-polarization, as was initially thought, but on the spacer material and the nature of the interfaces (i.e. roughness, electronic bands). High tunneling magnetoresistance ratios have been estimated for ferromagnetic metal(FM)/semiconductor(SM) multilayers, based on electronic bands calculations. However, very low TMR ratios have been measured in FM/SM/FM tunnel junctions. These results coud be originated in the existence of a ferromagnetic coupling between the iron layers. Therefore, the understanding of exchange coupling and other interactions in these heterostructures will also serve to improve its magnetoresistive properties. Our work is focused on the study of the magnetic coupling and magnetic anisotropies in FM/SM/FM sandwiches, based on ferromagnetic resonance experiments. This experimental technique is one of the most developed to study magnetic materials. The dependence of the resonance frequencies on the energy density function of the sample, provides us with all the essential parameters describing the magnetic properties of the films.