Pc. Fannin et al., Wide-band complex magnetic susceptibility measurements of magnetic fluids as a function of temperature, J MAGN MAGN, 201, 1999, pp. 91-94
Measurements of the complex magnetic susceptibility over the frequency and
temperature ranges of 2 MHz-6GHz and 20 to -100 degrees C, respectively, ar
e reported for the first time for a magnetic fluid. The fluid used was a co
lloidal suspension of magnetite particles of median diameter 9 nm in a hydr
ocarbon oil (isopar m).
Resonance was observed and found to increase from approx 1.5 GHz to 3.3 GHz
in the temperature range 20 to - 50 degrees C. The increase in resonant fr
equency is attributed to a decrease in thermal fluctuations with decrease i
n temperature.
At frequencies below approximately 19 MHz, a significant drop in chi'(omega
) with decrease in temperature over the temperature range 20 to -100 degree
s C, is observed and is attributed to the changes in the Neel and Brownian
relaxation processes. Below - 60 degrees C, the temperature at which the su
spension becomes solid, Brownian relaxation ceases to exist. (C) 1999 Elsev
ier Science B.V. All rights reserved.