Magnetization Reversal in Concave Iron Nano-Superellipses

Emre Öncü,Andrea Ehrmann

doi:10.3390/condmat6020017

Abstract

Square magnetic nanodots can show intentional or undesired shape modifications, resulting in superellipses with concave or convex edges. Some research groups also concentrated on experimentally investigating or simulating concave nano-superellipses, sometimes called magnetic astroids due to their similarity to the mathematical shape of an astroid. Due to the strong impact of shape anisotropy in nanostructures, the magnetization-reversal process including coercive and reversibility fields can be expected to be different in concave or convex superellipses than that in common squares. Here, we present angle-dependent micromagnetic simulations on magnetic nanodots with the shape of concave superellipses. While magnetization reversal occurs via meander states, horseshoe states or the 180° rotation of magnetization for the perfect square, depending on the angle of the external magnetic field, more complicated states occur for superellipses with strong concaveness. Even apparently asymmetric hysteresis loops can be found along the hard magnetization directions, which can be attributed to measuring minor loops since the reversibility fields become much larger than the coercive fields.

Highlights

Ferromagnetic nanoparticles can be used in a broad range of applications, especially in data storage and spintronics [1,2,3,4], and in energy devices, for drug delivery, and hyperthermia treatment [5,6,7,8]
Many research groups investigated round or square magnetic nanodots as a special shape of nanoparticles, often with round or square inplane symmetry, which often show magnetization reversal via vortex states, a behaviour that is advantageous for data storage due to the strongly reduced inplane stray fields [9,10,11,12,13]
Loops and magnetization reversal of some chosen angles, (MT) were calculated, and screenshots were taken duringmagnetization the magnetization-reversal simulated for SE0

Summary

Introduction

Ferromagnetic nanoparticles can be used in a broad range of applications, especially in data storage and spintronics [1,2,3,4], and in energy devices, for drug delivery, and hyperthermia treatment [5,6,7,8]. There are several ferri- or ferromagnetic metal oxides of which the energy band gaps can be tailored by varying the contents of different metal ions [14,15,16]. Other shapes of magnetic nanodots, reached intentionally or by undesired shape modifications due to the lithography process, show a broad range of different magnetizationreversal processes and magnetic states. Structures with open cores can show horseshoe states, onion states, and various other magnetic states [21,22,23]

Methods

Results

Conclusion