Synthesis and properties of magnetic films with controlled anisotropy

Several types of magnetic films containing rare earth and/or transition metals are made by dc magnetron sputtering. Deposition conditions are varied and underlayers are used to control the magnetic anisotropy respective to the film geometry. In the case of Co/Cr multilayers, in-plane anisotropy is obtained with high coercivity over a wide range of Co and Cr thicknesses. The deposition conditions can be chosen so the Co/Cr multilayer films have hcp Co layers aligned with the (110) crystal planes in the film plane following the bcc (100) textured Cr underlayer. The films consist of columnar grains of size about 400 A to 800 A which is in the range of single-domain particle size. The interruption of the magnetic layer by Cr layers, the proper crystal orientation, a large amount of interfacial diffusion and appropriate microstructure are responsible for the high coercivity. Numerical calculations of hysteresis loops have been performed based on a modified Stoner-Wohlfarth model and calculated 2-D results agree qualitatively with the experimental data. The magnetization reversal is likely dominated by the rotation of single-domain grains with interactions among them. Study of interaction by using the $\Delta$M technique indicates a weak ferromagnetic exchange interaction among the grains. SmFe$\sb{12}$ films with ThMn$\sb{12}$ structure and possibly with a minor part of disordered TbCu$\sb7$ structure and/or $\rm Th\sb2Zn\sb{17}$ structure are obtained with perpendicular anisotropy. Films are nitrogenated in-situ by annealing at elevated temperatures under nitrogen atmosphere. After nitrogenation the saturation magnetization and Curie temperature increase while the anisotropy field and coercivity become smaller along with a volume expansion of about 5.3%. Perpendicular anisotropy is also obtained for Nd(FeTi)$\sb{12}$ films with the ThMn$\sb{12}$ tetragonal structure. Upon nitrogenation the crystal unit cell volume expands about 3.6% and the anisotropy field, coercivity, saturation magnetization and Curie temperature all increase substantially. Thus these films are very good candidates for permanent-magnet film applications. Various magnetization reversal mechanisms are studied to explain the observed magnetic behavior. The aim of this work is to make films with controlled anisotropy and microstructure, and study the correlation between some of the intrinsic and extrinsic, structural and magnetic properties