Voltage-driven 90 switching of bulk perpendicular magnetic anisotropy in ferrimagnets

Rare earth-transition metal ferrimagnets, featuring antiferromagnetically coupled, inequivalent magnetic sublattices, have garnered increasing interest in the burgeoning field of ferrimagnetic spintronics. However, controlling their magnetism with low voltages,a key to reducing power consumption,remains challenging, particularly due to the poorly understood mechanisms underlying bulk perpendicular magnetic anisotropy (PMA). Here, we introduce a method involving voltage-driven hydrogen insertion into interstitial sites between Tb and Co atoms, selectively perturbing the atomic structure and enabling ultra-low-voltage (1.2 V) switching of bulk PMA to in-plane directions in ferrimagnetic films. Combining experimental and theoretical analysis, we find that the anisotropy switching originates from the reorientation of Tb orbital moments induced by the distortion of the crystal field. Initially aligned along Tb-Co bonding directions, the easy magnetization axis undergoes reorientation and switches by 90 deg,as substantiated by ab-initio calculations. Our study not only establishes the groundwork for voltage-controlled magnetic anisotropy in ferrimagnetic films, facilitating the development of electrically-programmable ferrimagnetic spintronics, but also elucidates the atomic origins of PMA in amorphous ferrimagnets, shedding light on a long-standing question in this field.