ANISOTROPY AND MAGNETOSTRICTION OF 4d AND 5d TRANSITION-METAL IONS IN GARNETS AND SPINEL FERRITES

Resum& - Grgce a leur couplage spin-orbite trb fort, les ions des series 4d et 5d apportent une contribution importante aux proprietks anisotropes des ferrites et grenats. En particulier les ions ds en Ctat de spin bas, tels que Ru3+, Os3+, Rh4+ et Ir4+, presentent un interkt particulier car leurs niveaux d'tnergie les plus bas, qui determinent leurs proprieth magnetiques, ont une structure simple. Les contributions A I'anisotropie et a la magnetostriction peuvent 6tre explicitement calcul6es dans le cadre de la theorie A un ion et dans la gamme de tempkratures 0 < T < Tc, ce qui n'est plus possible pour d'autres ions anisotropes. La comparaison entre thtorie et resultats ex+rimentaux fournit un excellent accord dans les cas choisis, ce qui Ctaye l'hypothese simple du modele A un ion dans le cas d'un systhme magnktique ordonne. Abstract. - Some 4d and 5d transition-metal ions are expected to contribute significantly to the anisotropic properties of ferrites and garnets owing to their strong spin-orbit coupling. In particular the low-spin d5 ions such as Ru3+, Os3-I-, Rh4+ and Ir4+ are of special interest since they exhibit a very simple level structure of their lowest energy levels which determine the magnetic behaviour. For these ions the contributions to anisotropy and magnetostriction can be calculated explicitely within the single-ion theory for the complete temperature range (0 < T < Tc) in contrast to other strongly anisotropic ions. The comparison of the theory with experimental results yields excellent agreement for selected cases supporting the simple conception of the single-ion model in magnetically ordered systems in correspondence to paramagnetic materials.