Reversing the circulation of ferromagnetic nanodisks with a local circular magnetic field

Abstract

Ferromagnetic nanodisks have a unique closed-flux vortex state with two degrees of freedom that results in four different magnetization states that are degenerate in energy and stable against thermal fluctuations. Such disks could be interesting for magnetic memory devices if the independent switching of each degree of freedom can be realized. Polarity switching of the vortex core has been demonstrated, but it is difficult to manipulate switching of the vortex due to the high symmetry of the structure. In this work, we reverse the circulation direction of a circular ferromagnetic nanodisk by applying a local circular Oersted field via a metallic atomic force microscope tip placed at the center of the disk. The resulting field reverses the circulation of the vortex without switching the orientation of the core. Switching of the vortex is accomplished by the sudden increase in the current that occurs when there is dielectric breakdown of a thin insulating layer on top of the disk. Micromagnetic simulations indicate that a line current concentrated in the center of a nanodisk can reverse the magnetization of the disk at a value over one order of magnitude smaller than the current required if the current is instead uniformly distributed across the cross section of disk. These results can be applied to reducing the switching current in circularly symmetric device structures.

Electric Control of Exchange Bias at Room Temperature by Resistive Switching via Electrochemical Metallization

“…It plays an important role in the practical application of spintronic devices . At present, magnetic memory devices mainly use the Oersted field directly generated by a current or spin-transfer torque induced by a spin-polarized current to reverse the magnetic moment and therefore realize the data storage, but their power consumption is very high . However, the continuous miniaturization of devices and integrated circuits demands much lower power consumption.…”

“…2 At present, magnetic memory devices mainly use the Oersted field directly generated by a current or spin-transfer torque induced by a spin-polarized current to reverse the magnetic moment and therefore realize the data storage, but their power consumption is very high. 3 However, the continuous miniaturization of devices and integrated circuits demands much lower power consumption. Electric field (E-field) control of EB provides a feasible way for the full electric control of magnetism, which is appealing for developing highly energy-efficient spintronic devices.…”

Characteristics and controllability of vortices in ferromagnetics, ferroelectrics, and multiferroics

“…Moreover, spin-transfer torque can play an important role, i.e. either assist or act against the Oersted field, during the switching process [421,422]. By tailoring the structure and size of the nanopillar, the assistance of the spin-transfer torque on vortex chirality switching can be significant.…”

Nanocavity-Mediated Fast Magnetic Vortex Core In-Situ Switching by Local Magnetic Field

“…The application of vortex-based devices requires the perfect controllability of the polarity and/or the circulation. Attempts have been made to reverse the vortex circulation deterministically by lifting the degeneracy between the clockwise and counterclockwise circulation through the use of shape-engineered nanomagnets, [3−6] inhomogeneous magnetic field, [7,8] current induced Oersted field [9,10] and bi-component magnetic nanodisks. [11] For a VC memory, [12,13] an energy efficient as well as fast VC switching process needs to be provided.…”