Title

A Method for Measuring the Néel Relaxation Time in a Frozen Ferrofluid

Document Type

Article

Publication Date

7-25-2015

Publication Title

Journal of Applied Physics

Abstract

We report a novel method of determining the average Néel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude (H0=20H0=20 kA/m) driven at frequencies of 171 kHz, 232 kHz, and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Néel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with previously published results.

Volume

118

Issue

6

DOI

https://doi.org/10.1063/1.4928202

ISSN

0021-8979

Comments

ESSN: 1089-7550

Rights Statement

© 2015 AIP Publishing LLC.

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