Dynamic bias effects: Transient anomalous Hall behavior in voltage-controlled magnetic anisotropy of CoFeB/Mg/MgO structures

Voltage-controlled magnetic anisotropy (VCMA) has emerged as a potential solution to significantly reduce the power consumption of next-generation magnetic random-access memory (MRAM). There are still great challenges in manipulating the VCMA effect and achieving a large VCMA value. In this work, we utilized Mg insertion to enhance VCMA and revealed the transient anisotropy variation characteristics during the voltage-controlled process in CoFeB/MgO based magnetic tunnel junction structures. The hysteresis loops extracted from the anomalous Hall effect show a split during multiple scans at different voltages, where the amplitude of the split changes regularly with the voltage and scanning times. There are more obvious splitting states in the cases of negative voltage compared to positive voltage, and no influence is shown in the situation with zero voltage. This transient state persists, and it is an intermediate state that gradually stabilizes and eventually reaches equilibrium after several scans; this behavior is related to the interfacial migration of oxygen ions due to the combined influence of the external voltage and high Mg-O binding energy. Our work provides insights into the underlying mechanisms of VCMA in CoFeB/MgO based structures, which provides a foundation for further study of the magnetic anisotropy manipulation in the practical application of MRAM.