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 omega(H). Owing to asymmetric resonance characteristics between the two orthogonal eigenmodes at omega(H) close to the vortex eigenfrequency omega(D), the use of H-CCW (H-CW) with omega(H) similar to omega(D) allows us to selectively and reliably switch, with sufficiently low field strengths as small as similar to 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.close9