Magnetoresistive system with concentric ferromagnetic asymmetric nanorings

Abstract

A structure consisting of two concentric asymmetric nanorings, each displaying vortex remanent states, is studied with micromagnetic calculations. By orienting in suitable directions, both the asymmetry of the rings and a uniform magnetic field, the vortices chiralities can be switched from parallel to antiparallel, obtaining in this way the analogue of the ferromagnetic and antiferromagnetic configurations found in bar magnets pairs. Conditions on the thickness of single rings to obtain vortex states, as well as formulas for their remanent magnetization are given. The concentric ring structure enables the creation of magnetoresistive systems comprising the qualities of magnetic nanorings, such as low stray fields and high stability. A possible application is as contacts in spin injection in semiconductors, and estimations obtained here of magnetoresistance change for a cylindrical spin injection based device show significant variations comparable to linear geometries.

Numerical simulation of magnetic properties for Co asymmetric nanorings

“…Among the study of magnetic nanorings, much attentions have been draw to the properties of symmetric system, [7][8][9][10] while asymmetric structure have important applications in biomedical and magnetism fields. For example, some asymmetric nanoparticles interact with cells and extracellular environment to produce a range of biological effects 11 ; Janus colloidal particles have tunable and controllable asymmetric structure, which controls their physical and chemical properties to the nanoscale 12 ; asymmetric silver nanoparticle aggregates will benefit for resolving light handedness, meanwhile, the nanoparticle trimmer can enhance circular dichroism and optical activity, 13 some concentric asymmetric nanorings show significant variations comparable to linear geometries, which can be used as contacts in spin injection in semiconductors 14 ; and so on.…”

“…However, the existing study mostly focused on experiment [4][5][6][7][8][9][10][11][12][13] and micromagnetics methods. [14][15][16] The simulation about asymmetric nanorings using Monte Carlo method is seldom reported. The reason for this phenomenon is that the simulation of dipole energy is complicated, and the computer will spend the bulk of program's time to calculate dipole energy.…”

Dynamic susceptibility of concentric permalloy rings with opposite chirality vortices

“…33 Concentric rings have also been considered as contacts in spin injection devices for semiconductors which can utilise the properties of magnetic nanorings, such as low stray fields and high stability. 34 For a single thin-ring structure at remanence, a stable bidomain state called the onion state is observed with head-tohead and tail-to-tail domain walls. 20,35,36 When a magnetic field is applied parallel to the plane of the ring, one of the domain walls de-pins and moves toward the other domain until the onion state is annihilated and forms a vortex domain structure.…”