Reliable low-power control of ultrafast vortex-core switching with the selectivity in an array of vortex states by in-plane circular-rotational magnetic fields and spin-polarized currents

The authors investigated the technological utility of counterclockwise (CCW) and clockwise (CW) circular-rotating fields (H-CCW and H-CW) and spin-polarized currents with an angular frequency omega(H) close to the vortex eigenfrequency omega(D), for the reliable, low-power, and selective switching of the bistate magnetization (M) orientations of a vortex core (VC) in an array of soft magnetic nanoelements. CCW and CW circular gyrotropic motions in response to H-CCW and H-CW, respectively, show remarkably contrasting resonant behaviors, (i.e., extremely large-amplitude resonance versus small-amplitude nonresonance), depending on the M orientation of a given VC. Owing to this asymmetric resonance characteristics, the H-CCW (H-CW) with omega(H)similar to omega(D) can be used to effectively switch only the up (down) core to its downward (upward) M orientation, selectively, by sufficiently low field (similar to 10 Oe) and current density (similar to 10(7) A/cm(2)). This work provides a reliable, low power, effective means of information storage, information recording, and information readout in vortex-based random access memory, simply called VRAM. (c) 2008 American Institute of Physics.