High-temperature magnetic properties of noninteracting single-domain Fe3O4 nanoparticles

TL;DR

This study investigates the high-temperature magnetic behavior of 40-nm Fe3O4 nanoparticles coated with SiO2, demonstrating that they behave as noninteracting single-domain particles with anisotropy constants close to bulk values.

Contribution

It provides experimental validation that SiO2-coated Fe3O4 nanoparticles act as noninteracting single-domain particles and accurately estimates their anisotropy constants and particle size from magnetic data.

Findings

Effective anisotropy constant K is (1.68 ± 0.17) × 10^5 erg/cm^3.

Mean particle diameter from magnetic data matches TEM measurements.

SiO2 coating suppresses interparticle interactions, enabling single-particle magnetic analysis.

Abstract

Magnetic measurements have been performed on 40-nm sphere-like Fe3O4 nanoparticles using a Quantum Design vibrating sample magnetometer. Coating Fe3O4 nanoparticles with SiO2 effectively eliminates magnetic interparticle interactions so that the coercive field HC in the hightemperature range between 300 K and the Curie temperature (855 K) can be well fitted by an expression for noninteracting randomly oriented single-domain particles. From the fitting parameters, the effective anisotropy constant K is found to be (1.68 \pm 0.17) \times 105 erg/cm3, which is slightly larger than the bulk magnetocrystalline anisotropy constant of 1.35 \times 105 erg/cm3. Moreover, the inferred mean particle diameter from the fitting parameters is in quantitative agreement with that determined from transmission electron microscope. Such a quantitative agreement between data and theory suggests that the assemble of our SiO2-coated sphere-like Fe3O4 nanopartles represents a good system of noninteracting randomly-oriented single-domain particles.