HYSTERESIS EFFECT IN A COLLOIDAL SUSPENSION OF MAGNETIC BEADS
Pages 10-18
P.C. Fannin
Abstract
Results of the measurement of the frequency and field dependence of the complex magnetic susceptibility, χs(ω) = χ's(ω) -iχ"s(ω), of a water based colloidal suspension of 200nm magnetic beads containing single domain maghemite( γFe203) nanoparticles, are presented.
Measurements are performed over the frequency range 200 Hz to 1 MHz whilst the polarizing field, H, is varied over the range 0-13.6 kA/m, initially in a forward direction, and then in a reverse direction and from a plot of the static susceptibility, χ0S, against H, the existence of a hysteresis effect is confirmed.
Under the increasing polarizing field an absorption peak is detected in the imaginary susceptibility component at frequencies fmax between 1.26 and 2.15 kHz. It is confirmed that the absorption peak can be attributed to the Néel relaxation of the inner maghemite nanoparticles.