  In our earlier work [Appl. Phys. Lett. 92, 022509 (2008)], we proposed
nonvolatile vortex random access memory (VRAM) based on the energetically
stable twofold ground state of vortex-core magnetizations as information
carrier. Here we experimentally demonstrate reliable memory bit selection and
low-power-consumption recording in a two-by-two vortex-state dot array. The bit
selection and core switching is made by flowing currents along two orthogonal
addressing electrode lines chosen among the other crossed electrodes. Tailored
pulse-type rotating magnetic fields are used for efficiently switching a vortex
core only at the intersection of the two orthogonal electrodes. This robust
mechanism provides reliable bit selection and information writing operations in
a potential VRAM device.
