Magnetic coupling in amorphous bilayers and sandwiches: (RCo)/Y/(RCo)' (R: Y, Gd)

摘要

The magnetic behaviour of amorphous (RCo)/(RCo)' bilayers and the influence of an optional intermediate layer have been studied. In the first analysed bilayer, the monolayers have the same M_s and competing individual anisotropies, with their anisotropy axes mutually orthogonal. The magnetic coupling of YCo_2 (40 nm)/Y/YCo_2 (40 nm)', for Y layer thickness in the 0-40 nm range, has been analyzed by bulk magnetometry and Magneto-Optic Kerr Effect. The exchange coupling produces that the easy axis of both YCo_2 layers are collinear when the intermediate Y layer is not present. On the other hand, for Y layer 2 nm in thickness, a magnetostatic coupling is observed; and, for Y intermediate layer thick enough (40 nm), no magnetic coupling is present. The second system studied is Gd_xCo_(1-x)/Gd_x'Co_(1-x) (0.21 <=x, x'<= 0.38). In this case the system is a Ferrimagnetic/(Ferrimagnetic)' bilayer where each individual layer has different compensation temperature. In particular for, Gd_(0.38)Co_(0.62)/Gd_(0.21)Co_(0.79), the Gd magnetic subnetwork dominates at room temperature in Gd_(0.38)Co_(0.62) (T_(comp)>300 K), while the opposite is found for Gd_(0.21)Co_(0.79) (T_(comp)=230 K). The strong Co-Co exchange interaction at the bilayer interface leads to a 'macroscopic ferrimagnet behaviour'. The magnetization processes of this bilayer have also been studied. Reversible coherent rotation of the magnetization is found when the field is applied perpendicular to the easy axis of the bilayer.