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It is commonly known that the coercivity (Hc) of the rare-earth/transition-metal (RE–TM) compound is tuned based on the varying RE content as compared to the TM component. The drawback of this approach is that the Hc changes are permanent. In this work, we investigate the coercivity behaviors of the GdFeCo/Hf/MgO heterostructure where the heavy metal Hf layer is inserted in the middle not only to convert charge current into spin current but also to prevent the oxygen diffusion effect. A strong geometry dependence of coercivity detected on Hall bar devices is attributed to the intrinsic properties of GdFeCo and elucidates that the oxidation issue from MgO on GdFeCo is prevented. By selecting a proper Gd content, we demonstrate that the coercivity can be altered flexibly in a wide range H c max / H c min ≈ 200 % via electric current. We develop a simple model to simulate the roles of Joule heating and spin–orbit torques in the novel behaviors of coercivity. It is verified that the excellent magnetic characteristics of GdFeCo are still preserved while manipulating coercivity by the electric current. Our findings broaden the new magnetic behaviors of RE–TM alloys, making them attractive for tunable magnetic anisotropy. [ABSTRACT FROM AUTHOR]

We investigate the Hf/GdFeCo bilayer with the MgO cap layer for both rare earth (RE)-rich and transition metal (TM)-rich configurations of the ferrimagnetic sublattice in the presence of the perpendicular field. We study the coercivity using the anomalous Hall effect (AHE) technique by multiple measurements on the same sample. In the first set of measurements and at low electric currents, coercivity sharply drops because of the oxygen diffusion at the interface between MgO and GdFeCo when the AHE probe current is applied. During the subsequent measurements on the RE-rich sample, we observe a moderate decrease in coercivity at low currents and the coercivity increases in a high current range. Such nonlinear dependence of coercivity on electric current can be explained by the competing interplay of the spin–orbit torque (SOT) and the Joule heating effects. On the other hand, for the TM-rich case, the SOT effect is observed over a widely applied current range. [ABSTRACT FROM AUTHOR]