Micromagnetic study of the vortex state in sub-micron iron discs

Ludgero Peixoto,J.P Araújo,C Sousa,D Navas,B.G Almeida,J Agostinho Moreira

doi:10.1051/epjconf/202023305002

Abstract

Magnetic nanostructures have been widely studied due to its poten¬tial applicability into several research fields such as data storage, sensing and biomedical applications. In this work, micromagnetic simulations (mumax3) of sub-micron iron discs are performed for different normalized inter-dot distance (distance/diameter), to better understand the magnetic behaviour of these nanos-tructures. Two sets of samples were studied: ideal circular discs and disc-shaped nanostructures (based on images of real samples). By analyzing the nucleation and annihilation fields and the magnetic susceptibility, it was found that the (ideal) discs could be considered as isolated for inter-dot distances greater than twice the raidus of the disc (2R). The difference in the shape of the disc-shaped nanostructures resulted in an in-plane anisotropy, noticeable on the hysteresis loops for different directions.

Highlights

Magnetic nanostructures are, currently, the focus of several research fields, such as data storage, sensing and biomedicine
The focus of several research fields, such as data storage, sensing and biomedicine. One subset of these nanostructures are discs that present a magnetic vortex state in remanence. These discs can be used for data storage [1] and for cancer therapy, by magneto-mechanically induced cell death [2]
The vortex state is a direct result of the geometry and aspect ratio of the nanostructure

Summary

Introduction

The focus of several research fields, such as data storage, sensing and biomedicine. In the case of the discs, the minimization of energy causes the spins to be in a curling state, gradually changing direction They start starting parallel to the borders of the disc, remaining in-plane until there is a point where it is energetically favourable for the spins to point either up or downwards, forming the vortex core [3, 4]. The program starts by issuing a random magnetic state in the desired geometry and taking a snapshot of it, following up by minimizing the energy which results in the fundamental state, recorded After this step, the discs are submitted to a magnetic field loop that forces positive and negative saturation, recording the data in a table. RK45, the Dormand-Prince method, offers 5-th order convergence and a 4-th order error estimate used for adaptive time step control [6]

Ideal discs

Magnetic susceptibility

Irregular disc-shaped nanostructures

Concluding remarks