Magnetic properties of cubic FeCo nanoparticles with anisotropic long chain structure

Jinming Liu,Jian-Ping Wang,Kai Wu

doi:10.1063/1.4945042

Abstract

Cubic FeCo alloy nanoparticles (NPs) with body-centered cubic (bcc) phase were prepared using sputter based gas-condensation method. When the NPs formed long chain assemblies, the magnetic properties were quite different from that of well-dispersed NPs. Most of the well-dispersed NPs were superparamagnetic at room temperature while the long chain NP assemblies were ferromagnetic with coercivities around 765 Oe, which displayed quite different magnetic properties. The ferromagnetism of long chain NPs was from the exchange coupling between NPs, which eventually led to the transition from superparamagnetism (SPM) to superferromagetism (SFM). Zero-field-cooled (ZFC) and field-cooled (FC) curves were obtained and long chain NP assemblies displayed ferromagnetism at the temperature ranging from 10 K to 400 K. Time-dependent remanent magnetic moment curves also indicated that the long chain structure had better thermal stability due to the strong exchange coupling.

Highlights

Magnetic nanoparticles (NPs) have attracted researchers’ interests in the past decades due to their wide applications in hyperthermia,[1,2] drug delivery,[3,4] granular giant magnetoresistance,[5,6] catalysis recycling,[7,8] and so on
The ferromagnetism of long chain NPs was from the exchange coupling between NPs, which eventually led to the transition from superparamagnetism (SPM) to superferromagetism (SFM)
Two magnets were loaded on a substrate holder to align NPs during their deposition process in order to get the anisotropic long chain structure

Summary

INTRODUCTION

Magnetic nanoparticles (NPs) have attracted researchers’ interests in the past decades due to their wide applications in hyperthermia,[1,2] drug delivery,[3,4] granular giant magnetoresistance,[5,6] catalysis recycling,[7,8] and so on. The NP assemblies and chain structure have wide applications such as logic gates,[11] magnetic memory,[12] and shaping and diversifying components in magnetic devices.[13,14] So further understanding on the NPs assemblies with the presence of interactions is needed. We will focus on the magnetic properties of anisotropic long chain structure of high magnetic moment FeCo alloy NP assemblies. High magnetic moment NPs can provide more magnetic signals which is very helpful for their applications.[20] sputter based gas-condensation method was used to prepare cubic shape FeCo NPs. Two magnets were loaded on a substrate holder to align NPs during their deposition process in order to get the anisotropic long chain structure (named S1). The long chain FeCo NPs showed ferromagnetic behavior at a wide temperature range (10 K-400 K)

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSIONS

CONCLUSION