Multi-domain structures in spheroidal Co nanoparticles

N A Usov,M S Nesmeyanov

doi:10.1038/s41598-020-67173-5

Abstract

The structure of multi-domain micromagnetic states in hcp cobalt nanoparticles of spheroidal shape has been studied using numerical simulation in the range of diameters 20–200 nm. The single-domain diameters of the particles are determined depending on their aspect ratio. The complicated vortex structure of domain walls for two- and three-domain micromagnetic configurations is investigated. It has been shown that three domain states are actually strongly deformed two vortex states. In hcp cobalt particles of sufficiently large sizes two types of three-domain micromagnetic states with close total energies have been obtained. They differ in different magnetization directions of the exchange cores of the vortex domain walls. The remanent magnetization of particles has been calculated for two- and three-domain micromagnetic states. The single-domain diameters of fcc cobalt nanoparticles with cubic type of magnetic anisotropy were also calculated.

Highlights

The structure of multi-domain micromagnetic states in hcp cobalt nanoparticles of spheroidal shape has been studied using numerical simulation in the range of diameters 20–200 nm
The following magnetic parameters were used in the numerical simulation of the magnetization distributions in hcp cobalt nanoparticles with a uniaxial type of magnetic anisotropy: saturation magnetization Ms = 1400 emu/cm[3], uniaxial magnetic anisotropy constant K = 4.3 × 106 erg/cm[3], exchange constant C = 2 A = 2.6 × 10−6 erg/cm[1,40,41]
The easy axis of magnetic anisotropy is assumed to be parallel to the particle axis of symmetry, which is directed along the Z axis of Cartesian coordinates

Summary

Introduction

The structure of multi-domain micromagnetic states in hcp cobalt nanoparticles of spheroidal shape has been studied using numerical simulation in the range of diameters 20–200 nm. In hcp cobalt particles of sufficiently large sizes two types of three-domain micromagnetic states with close total energies have been obtained. They differ in different magnetization directions of the exchange cores of the vortex domain walls. Stapper[19] computed a one-dimensional magnetization distribution in a cobalt sphere with uniaxial anisotropy subdividing the particle into a large number of thin parallel slices He showed that the energy of the two-domain state became lower than that of the uniform magnetization if the diameter of the sphere exceeded a critical value, Dс0 = 76.0 нм. Similar calculations were carried out [21] for a nanoparticle with cubic magnetic anisotropy

Methods

Results

Conclusion