Researchers have designed a new kind of magnetic memory called frequency-controlled magnetic vortex memory. It takes advantage of magnetic vortices' ability to store binary information as positive or negative core polarities, which can be controlled by simply changing the frequency of the rotating vortex cores of the nanodots.
The concept of using magnetic nano-objects to store information for magnetic-RAM is already known, but it’s been difficult to find a mechanism to reverse the magnetization inside individual nano-objects. The researchers achieved this reversal by using microwave pulses in combination with a static magnetic field. In this scheme, large and small rotating core frequencies are associated with positive and negative core polarities, respectively. In a positive core polarity, the core is parallel to the applied magnetic field, while in a negative core polarity, the core is antiparallel to the applied magnetic field. An extremely sensitive magnetic resonance force microscope (MRFM) is used to address the resonant frequency of magnetic nanodots’ vortex core rotations, allowing the researchers to control the polarity states of individual nanodots.
The researchers’ memory design consists of an array of magnetic nanodots and an electromagnet that generates a static magnetic field perpendicular to the array of dots. The MRFM's small (800-nanometer-diameter) magnetic probe can scan the one-micrometer-diameter nanodots and locally control this magnetic field.