Separated Edge-Soliton-Mediated Dynamic Switching of Vortex Chirality and Polarity

Abstract

Magnetic vortices are characterized by the senses of in-plane magnetization chirality and by the polarity of the vortex core. The electrical control of vortex polarity and chirality is highly demanded not only for fundamental understanding on spin dynamics in nano-disks under different circumstances, but also for technological applications, such as magnetic non-volatile memories and spin torque oscillators for neuromorphic computing. Here we report a novel approach that enables one to electrically control both the vortex chirality and polarity with low energy consumption. Thorough micromagnetic simulations, we show that in thin nano-disks of diameter larger than 160 nm, with the presence of current-induced Oersted field, the dynamic transformation of the edge solitons is able to efficiently switch both vortex chirality and polarity with low current under certain circumstances. We then developed an approach to directly write any of the four vortex states by electrical current pulses from a random state. We further investigated the switching phase diagram as a function of disk diameters. The results show that the switching process is highly size-dependent. As disk diameter is smaller than 160 nm, the switch of VC chirality and polarity always takes place at the same time, resulting in an unchanged handedness before and after switch. Furthermore, the critical switch current can be as low as 6 2 3 10 / cm A × , indicating a possible way for low current switch of vortex chirality in small disks.defines the handedness of the vortex with 1 CP = and 1 CP = − being catalyzed as left and right handed vortices, respectively. Being one of the most interesting magnetic soliton, vortex can be used as an information carrier and is currently attracting much more attention for a number of applications. Magnetic vortex have been proposed as memory bit in non-volatile storage for many years [3,4], for its multi-bit information storage and high stability [5,6]. Very recently, vortex was introduced as a building block for a robust sensor application in the automotive industry [7], where a large linear range is discovered. In addition, vortex-based spin torque nano-oscillators have been demonstrated being building blocks for neuromorphic computing, which is one of research topics towards low-power artificial intelligence application [ 8 , 9 ]. A full understanding on the electrical control of vortex dynamics and the switching process is a key towards those applications. In the past decades, great efforts have been made for searching effective methods to control the vortex polarity and chirality.The VC is very stable, and a static field of above 0.5 T field is required to switch its polarity, while to switch vortex chirality requires even more energy [5,6]. Fortunately, further studied showed that it can be efficiently switched through a dynamic process [10].When excited, the VC will be driven into gyrotropic precession, and polarity reversal happens when the VC reaches a certain critical velocity [ 11,12,13], through the formation and...

Toroidal Order in Magnetic Metamaterials

“…Here, VRAM (vortex magnetic random access memory) has been discussed as a high-density magnetic data storage 238 that allows the encoding of binary information in the handedness of the magnetic vortex state 239,240 . Moreover, a four-state multi-bit memory has been realised using the handedness (clockwise and counter-clockwise whirled magnetic state) on the one hand and the magnetisation direction of the vortex core (up-or down-magnetised state) on the other hand 241,242 . Because of the inherently weak coupling between the elements, crosstalk is negligible by design.…”

“…Because of the inherently weak coupling between the elements, crosstalk is negligible by design. Control over and read-out scenarios for magnetic vortex states have been proposed and experimentally realised by resonantly exciting a vortex-core gyration mode via radio frequency pulses 229,[241][242][243][244][245][246][247][248][249][250] , via spin-transfer torque 242,[251][252][253] , by a piezoelectric approach in a magnetostriction-coupled magnetoelectric heterostructure 254 , or by a geometrical 219,222,225,227,228,231,255,256 , field-induced 221 or interaction-mediator-based 257 asymmetry for accessing the vortex state with homogeneous fields. The applicability of VRAM, however, is not yet on an industrial level of production.…”

Chirality Switching in Ferromagnetic Nanostructures Via Nanosecond Electric Pulses

“…Despite the attractive potential of tailoring vortex states in nano magnets, a limited number of works have focused on chirality switching of these structures both experimentally and computationally. [ 14–18 ] One forthcoming major challenge is to achieve swift and repeatable control of magnetism in these structures and establish chirality switching in a time period desirably not exceeding a few nanoseconds. Generally, the vortex state is not a stable state in bulk: Order stability maps have been generated where chiral ferromagnetic states were shown to depend on the aspect ratios and geometry.…”

“…[ 19–23 ] In refs. [18–22], the phase stabilities of various ferromagnetic states in phase diagrams of nanostructures reveal that a unit must have a distinct aspect ratio to obtain a magnetic vortex state. If there is no shape anisotropy, the CW and CCW states are degenerate and they may emerge randomly as equilibrium states.…”

“…have reported polarity switching to occur simultaneously below a critical disc size whereby the method they used to simulate switching was passing a direct current along the disc normal driving an Oersted field. [ 18 ] Experimentally, due to the spatial variation of magnetic order, investigation of the polarity switching dynamics possesses challenges and is pursued in a limited number of attempts. [ 7 ]…”