A method for measuring the Néel relaxation time in a frozen ferrofluid

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 nanopar...

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Bibliographic Details
Published in:Journal of applied physics 2015-08, Vol.118 (6)
Main Authors: Tackett, Ronald J., Thakur, Jagdish, Mosher, Nathaniel, Perkins-Harbin, Emily, Kumon, Ronald E., Wang, Lihua, Rablau, Corneliu, Vaishnava, Prem P.
Format: Article
Language:English
Subjects:
Anisotropy
Applied physics
Chemical precipitation
Chemical synthesis
Energy absorption
Ferrofluids
Iron oxides
Magnetic fields
Nanoparticles
Organic chemistry
Relaxation time
Temperature
Temperature dependence
Time dependence
Transmission electron microscopy
X-ray diffraction
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Summary: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=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.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4928202