Magneto-transport and spin-reorientation in Pt/Co78Ho22 heterostructures near the sublattice compensation temperature

Metallic amorphous ferrimagnets of 3d transition metals (TMs) and rare earths (REs) with 4f electrons exhibit rich magneto-transport behavior due to the interplay between the 3d and 4f magnetic sublattices and their interaction with mobile charges. Tuning the TM and RE concentrations in the alloy can effectively modulate the compensation temperature, where the moments of the two sublattices point in the opposite direction leading to a net zero magnetization. Despite extensive magneto-transport studies in Gd- and Tb-based 3d–4f systems, Ho-based alloys remain comparatively underexplored, even though Ho possesses the largest orbital angular momentum (OAM) among the lanthanides. This unquenched OAM can strongly impact magnetic anisotropy and magneto-transport in ferrimagnetic heterostructures. Here, we have investigated the anomalous Hall resistivity (ρxyAHE), dc magnetization, and spin Hall magnetoresistance (SHMR) of Co78Ho22/Al films and a Pt/Co78Ho22/Al heterostructure deposited using multitarget magnetron sputtering. ρxyAHE of both systems shows a distinct sign reversal and prominent wing-shaped hysteresis loops in the vicinity of the compensation temperature (Tcomp), which is accompanied by the minimum saturation magnetization near Tcomp. Furthermore, the SHMR in Pt/Co78Ho22/Al films is enhanced due to the Pt layer. These HM interface-induced prominent features of magneto-transport are addressed in the light of the existing theories of spin-flop transitions, spin–orbit torque, and microscopic phase separation, which may lead to the formation of 3d and 4f magnetic clusters in the film.