Coercivity in amorphous Tb–Fe alloys

The perpendicular magnetic anisotropy, coercive field, and initial magnetization curves of amorphous TbxFe1−x (x between 0.15 and 0.32) were measured at room temperature for samples prepared under a wide variety of preparation conditions, including both e-beam co-evaporation and dc magnetron cosputtering. The effect of growth temperature, annealing, and thickness were investigated. The perpendicular magnetic anisotropy shows little dependence on substrate type, sample thickness, or details of the deposition such as sputtering or e-beam evaporation, but is strongly dependent on growth temperature, increasing with increasing growth temperature up to nearly 300 °C. Coercivity on the other hand is extremely dependent on microstructure, and hence, on details of preparation, substrate type, and thickness. It is much larger in evaporated films than in similarly prepared dc magnetron sputtered films. Normalized coercivity decreases monotonically with increasing growth temperature. The dominant mechanism appears to be domain wall pinning in the bulk of the film due to columnar microstructure. High growth temperature stabilizes the material against subsequent annealing which tends to eliminate the anisotropy and, more slowly, the coercivity.