Origin of reduced magnetization and domain formation in small magnetite nanoparticles

Zlatko Nedelkoski,Sara Majetich,Leonardo Lari,Samuel D Oberdick,Quentin M Ramasse,Vlado K Lazarov,Ryan A Booth,Demie Kepaptsoglou,Pedro L Galindo,Richard F L Evans,Tianlong Wen

doi:10.1038/srep45997

Abstract

Highlights

The structural, chemical, and magnetic properties of magnetite nanoparticles are compared
The experiments compared 12–14 nm diameter iron oxide nanoparticles synthesized by three well-established methods that were pioneered by the groups of Sun[17], Colvin[18] and Hyeon[19]
All three synthesis methods involve high temperature inert atmosphere decomposition in organic solvents, leading to monodisperse, highly crystalline, spherical particles coated with surfactants

Summary

Introduction

The structural, chemical, and magnetic properties of magnetite nanoparticles are compared. Aberration corrected scanning transmission electron microscopy reveals the prevalence of antiphase boundaries in nanoparticles that have significantly reduced magnetization, relative to the bulk. Strong antiferromagnetic interactions across antiphase boundaries support multiple magnetic domains even in particles as small as 12–14 nm. High resolution electron microscopy is used to identify subtle differences in three kinds of NPs, and atomistic spin calculations are used to reveal the origin of the reduced magnetization and its anomalous temperature dependence. While the detection of APBs requires sophisticated atomic resolution electron microscopy, we show that besides the reduced Ms, zero field cooled magnetization measurements can be used to identify types of NPs with a high density of these defects, and lower magnetization compared with that of single crystal NPs

Methods

Results

Conclusion