Low-Power Selective Control of Ultrafast Vortex-Core Switching by Circularly Rotating Magnetic Fields: Circular–Rotational Eigenmodes

We found novel dynamic properties of vortex gyrotropic motions in soft magnetic nanodots driven by oscillating in-plane magnetic fields. The elementary eigenmodes of the field-driven gyrotropic motions are found to be the two counterclockwise (CCW) and clockwise (CW) circularly rotating motions of a vortex core (VC) with respect to the corresponding CCW and CW circularly rotating fields (H _CCW and H _CW) of a certain angular frequency omegaH. Owing to asymmetric resonance characteristics between the two orthogonal eigenmodes at omegaH close to the vortex eigenfrequency omegaD , the use of H _CCW (H _CW) with omegaH ~ omegaD allows us to selectively and reliably switch, with sufficiently low field strengths as small as ~ 10 Oe, only the upward (downward) oriented VC to its downward (upward) one. The results promise a reliable, low-power, and effective means of information storage, recording, and readout, representing an advanced step toward realizing a new class of vortex-based random access memory (VRAM) devices.