The field induced magnetic anisotropy in amorphous Co-RE alloys films

The properties of the coherent anisotropy, formed by applying a magnetic field in the film plane during deposition, were studied in amorphous (Co_1-yZr_y)(RE)_x thin films, for various RE and deposition parameters. When RE=Pr,Nd,Dy and Tb an in-plane uniaxial anisotropy K_u is developed. The variations of K_u versus x, RE and measuring temperature are well explained by a single-ion anisotropy mechanism. The change of K_u with P_Ar and deposition temperature T was studied on Co_95-xZr₅Dy_x films and for 5<x<30. The variations of K_u with the P_Ar are due to an evolution of the local structure. K_u is maximum for the lowest T_d used (-100°C) and its value decreases continuously when T_d increases. When x>22 films with isotropic magnetic properties are obtained at T_d higher than T_crit=f(x). Structural investigations show that K_u is related to sites containing CoDy pairs. The data are explained by a model based on the bond orientational mechanism: In samples prepared at low T_d, K_u is related to the individual deformations of sites, while when thermal fluctuations are important, directional correlations of the sites are formed. The peculiar results observed for RE=Sm and Gd are due to the intrinsic properties of these RE