image: (a) A geometry of NiFe-BWO magnetoelectric thin film device with four planar electrodes. (b) The deterministically reversible reversal of single magnetic vortex circulation by bi-axial pulsed electric field. (c) The space-varying strain evolves as a function of pulsed electric field numbers. (d) Dynamic mechanism of magnetic vortex reversal. (e) Electric-field-controlled magnetic vortex based data-storage devices.
Vortex is ubiquitous in nature including spiral arms of galaxy, planet rotation, hurricane (tornado). A vortex is a typical and well-known magnetic domain structure in dimensionally confined nanostructures with a symmetry determined by its polarity and circulation. Reversible control of low-dimensional spin structures at nanoscale with low energy consumption is highly desirable for future applications of spintronic devices. Especially, magnetic vortex at nanoscale has been explored for the next-generation data-storage devices.
For the past decades, magnetic field and spin-polarized current have been employed to flip the core and/or reverse circulation of vortex. However, the electric-field deterministic control of a magnetic vortex, which offers much higher storage density and much lower power consumption, is challenging due to the absence of planar magnetic anisotropy of the spin structure.
Chinese researchers discover a deterministic reversal of magnetic vortex circulation in a Ni79Fe21 (NiFe) island on top of a layered-perovskite Bi2WO6 (BWO) thin film using an electric field. The space-varying strain from BWO film under a bi-axial planar electric field drives the magnetic vortex circulation reversal in this magnetoelectric device. Phase-field simulation directly reveals the mesoscale dynamic reversal mechanism: the traveling strain drags the vortex core from its center to the edge of the NiFe island, then a new core emerges with opposing vortex circulation, leading to the vortex circulation reversal.
This study provides a new framework to deterministically manipulate nanoscale chiral spin texture (vortex, skyrmions etc.) with ultralow-energy consumption. Especially in physical mechanism research, it revealed new magnetoelectric coupling mechanism for more efforts to realize the electric-field control of order parameters (charge, spin and orbital) in functional thin film devices in future.