Observation of double anomalous Hall polarity reversals with temperature in an ultrathin ferrimagnetic insulator

We report the observation of two temperature-driven polarity reversals of the anomalous Hall effect (AHE) in an ultrathin thulium iron garnet Tm3Fe5O12, TmIG and platinum (Pt) heterostructure, grown by scalable on-axis sputtering. Hall-bar devices fabricated from a 6-nm-thick, epitaxially strained TmIG film grown on (111) gadolinium gallium garnet exhibit polarity reversals of the anomalous Hall resistance at ∼81 and 124 K. A pronounced divergence of the coercive field is observed only at the lower temperature, indicating a compensation-like transition. True magnetic compensation has not previously been reported in TmIG owing to the weak exchange coupling between the Tm and Fe sublattices. We attribute the two polarity reversals to distinct physical mechanisms: a crossover in the dominant contribution to the AHE within the Pt layer, and a strain-induced modification of the magnetic structure of the TmIG layer, detected via the magnetic proximity effect. These results demonstrate strain as an effective control parameter for engineering proximity-induced magnetotransport in heavy-metal/rare-earth iron garnet heterostructures.