Sublattice magnetization driven anomalous Hall resistance of FeCoGd amorphous films

Measurements of magnetization [M(H, T)] and anomalous Hall resistance [R-xy(H, T)] are performed over a broad range of magnetic field (H) and temperatures (T) on sputter deposited 10 nm thick films of (FeCo)(1-x)Gd-x. The Gd content (x) in the films was changed by varying the Gd source power from 20 W to 50 W, in steps of 5 W. The saturation magnetization (M-s) of these films at 300 K shows a distinct minimum for the source power of 40 W. Measurements of M(H) for the 40 W sample at several temperatures establish full compensation of the antiferromagnetically coupled magnetic sublattices of Gd and FeCo at T-comp = 270 K +/- 10 K. The approach to compensation is characterized by the emergence of perpendicular magnetic anisotropy (PMA) and a diverging coercive field. The R-xy (H) of this sample, as well as of those prepared at 30 W and 50 W, scales with M(H) at T > T-comp and T < T-comp. However, this scaling fails in the vicinity of T-comp where the R-xy undergoes a sign reversal. Our analysis of these data in the framework of the existing models for R-xy(H, T) in ferrimagnets suggests that the role of spin disorder and its topological contribution to R-xy may be necessary to account for the observed behavior. A precise identification of T-comp is also important to stabilize technologically useful non-trivial spin textures and PMA in these systems.