Magnetization Reversal in Ferromagnetic Nanorings of Fourfold Symmetries

Abstract

Magnetic nanoparticles offer a broad spectrum of magnetization reversal processes and respective magnetic states, such as onion, horseshoe, or vortex states as well as various states including domain walls. These states can be correlated with stable intermediate states at remanence, enabling new quaternary memory devices storing two bits in one particle. The stability of these intermediated states was tested with respect to shape modifications, variations in the anisotropy axes, and rotations and fluctuations of the external magnetic field. In our micromagnetic simulations, 6 different stable intermediate states were observed at vanishing magnetic field in addition to the remanence state. The angular region of approx. 5 ∘ -12 ∘ between nanoring and external magnetic field was identified as being most stable with respect to all modifications, with an onion state as technologically best accessible intermediate state to create quaternary memory devices.

Magnetic Vortex States in Toroidal Iron Oxide Nanoparticles: Combining Micromagnetics with Tomography

“…Systematic studies of asymmetric particles include the analysis of artificially notched rings/disks, , slotted rings and spheres with conical bumps, but no simulated studies use real ring geometries although the experiments of Eltschka et al demonstrate a correlation between experimental geometry and magnetization configuration deserving further exploration. Furthermore, much of the literature in this area focuses on permalloy, nickel, cobalt, and pure iron particles in thin-film geometries geared toward switching mechanisms and vortex chirality for application in memory devices, ,− rather than toward the remanent state behavior in magnetite NPs for biomedical applications.…”