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

作者：Tackett Ronald J; Thakur Jagdish; Mosher Nathaniel; Perkins Harbin Emily; Kumon Ronald E; Wang Lihua; Rablau Corneliu; Vaishnava Prem P^*

来源：Journal of Applied Physics, 2015, 118(6): 064701.

DOI：10.1063/1.4928202

We report a novel method of determining the average Neel 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 dextrancoated 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 (H-0 = 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 160K 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 Neel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m(3), in agreement with previously published results.

• 出版日期2015-8-14