Role of anti-phase boundaries in the formation of magnetic domains in magnetite thin films

Roberto Moreno,Aleksandar Skeparovski,Alexander Gerber,Richard F L Evans,Sarah Jenkins,Zlatko Nedelkoski,Vlado K Lazarov

doi:10.1088/1361-648x/abe26c

Abstract

Anti-phase boundaries (APBs) are structural defects which have been shown to be responsible for the anomalous magnetic behavior observed in different nanostructures. Understanding their properties is crucial in order to use them to tune the properties of magnetic materials by growing APBs in a controlled way since their density strongly depends on the synthesis method. In this work we investigate their influence on magnetite (Fe3O4) thin films by considering an atomistic spin model, focussing our study on the role that the exchange interactions play across the APB interface. We conclude that the main atypical features reported experimentally in this material are well described by the model we propose here, confirming the new exchange interactions created in the APB as the responsible for this deviation from bulk properties.

Highlights

Anti-phase boundaries (APBs) are extended defects appearing in crystalline materials, created by a fractional displacement of the lattice constant between atomic planes
In this work we investigate their influence on magnetite (Fe3O4) thin films by considering an atomistic spin model, focussing our study on the role that the exchange interactions play across the APB interface
In this work we have modeled a magnetite system with and without APB defects using atomistic spin dynamics, focussing our analysis on the role that the exchange interactions play across the APB interface

Summary

Introduction

Anti-phase boundaries (APBs) are extended defects appearing in crystalline materials, created by a fractional displacement of the lattice constant between atomic planes. For the specific case of magnetite thin films, which is most promising materials for the generation of spintronic devices due it is half metallic character [14, 15] and high Curie temperature (TC = 860 K [16]), APBs seem to play a fundamental role on the magnetic properties of the system [8, 17] Both out of plane anisotropy [8] and fourfold in plane anisotropy [10] have been observed for different samples. We use an atomistic spin model to investigate their influence in magnetite thin films, focussing on explaining the anomalous saturation magnetization as well as the reason of why samples with more APBs have more magnetic domains, leaving the fact of observing different magnetic anisotropies for future work. Confirming APBs as responsible for the different magnetic behaviors observed in magnetite thin films grown with different methods opens the door of tuning the magnetic properties of this system by growing samples with APB defects in a controlled way

Atomistic spin model of magnetite

APB free magnetite system

Anti-phase boundary structure and properties

Saturation of anti-phase boundary defects

Temperature dependence of anti-phase boundary defects

Conclusions