Published online by Cambridge University Press: 15 December 1999
Measurements of the complex, frequency dependent susceptibility, χ(ω) = χ′ (ω) − i χ′′ (ω) over the frequency range 50 MHz to 15 GHz, of a surfacted ferrofluid comprising MnFe204 ferrite particles in dibutylphthalat (DBP), as a function of a biasing magnetic field arepresented. The biasing field was varied over the range 0 to 100 kAm−1, and has enabledaverage values of anisotropy constant, $\bar{K}$ , and anisotropy field $\bar{H}_{\rm A}$ forthe sample to be determined. Ferromagnetic resonance was exhibited for all values of the biasing field, covering the range 1.2 to 8.5 GHz, with the χ′ (ω) component of the susceptibility going negative in the GHz region.