Anisotropy-axis orientation effect on the magnetization of {\gamma}-Fe2O3 frozen ferrofluid

TL;DR

This study investigates how the orientation of magnetic anisotropy axes affects the magnetic properties and aging behavior of a frozen maghemite nanoparticle ferrofluid, revealing increased magnetization with alignment and differences in aging dynamics.

Contribution

It provides new insights into the influence of anisotropy-axis alignment on superparamagnetic and superspin glass states in ferrofluids, especially regarding aging behavior.

Findings

Aligned ferrofluid shows 2-4 times higher magnetization than random orientation.

Interaction energy and SSG phase temperature are insensitive to anisotropy alignment.

Distinct aging dynamics observed in aligned versus random states at low temperatures.

Abstract

The effect of magnetic anisotropy-axis alignment on the superparamagnetic (SPM) and superspin glass (SSG) states in a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (\gamma-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume fraction of ~15%. In the high temperature SPM state, the magnetization of aligned ferrofluid increased by a factor varying between 2 and 4 with respect to that in the randomly oriented state. The negative interaction energy obtained from the Curie-Weiss fit to the high temperature susceptibility in the SPM states as well as the SSG phase onset temperature determined from the linear magnetization curves were found to be rather insensitive to the anisotropy axis alignment. The low temperature aging behaviour, explored via "zero-field cooled magnetization" (ZFCM) relaxation measurements, however, show distinct difference in the aging dynamics in the anisotropy-axis aligned and randomly oriented SSG states.