Features and Peculiarities of Gate-Voltage Modulation of Spin-Orbit Interaction in FeB Nanomagnets: Insights Into the Physical Origins of the Voltage-Controlled Magnetic Anisotropy Effect

This letter systematically investigates the fundamental mechanisms driving the voltage-controlled magnetic anisotropy (VCMA) effect, with a focus on the dependencies of the anisotropy field and the strength of spin-orbit (SO) interaction on gate voltage, measured in Ta/FeB/MgO nanomagnets. Our findings reveal an intriguing opposite polarity in the gate-voltage dependencies of the anisotropy field and the coefficient of SO interaction across all studied nanomagnets. This discovery challenges the prevailing assumption that SO interaction is the primary contributor to the VCMA effect, instead suggesting that gate-voltage modulation of magnetization is likely the dominant factor, as its polarity aligns with the observed modulation of anisotropy. The modulation of magnetic anisotropy is governed by two major contributions with opposite polarities, which tend to counterbalance each other, reducing the overall VCMA effect. Optimizing this balance could significantly enhance the VCMA effect, offering a promising avenue for broadening its applications. In addition, our measurements confirm that gate voltage does not modulate the in-plane component of spin accumulation, providing further insights into the underlying mechanisms of the VCMA effect.