ELECTRON-SPIN RESONANCE-SPECTRA OF CERTAIN MAGNETIC FLUIDS

Electron spin resonance spectra of certain magnetic fluids are recorded at different temperatures. All the samples exhibited only one broad absorption line. Low temperature data are interpreted in formation of spin glass. Superparamagnetism will be exhibited by single domain particles below a critical size for which the relaxation time is much less than gyroprecession period of orbital magnetic moment. Hence the linewidth of superparamagnetic resonance is proportional to the volume V (below critical size) of the particle. In effect, one expects a narrow magnetic resonance signal and a few hundred oersted wide if the sample contains ultrafine particles in superparamagnetic state in an applied field H. One of the objects of the present work was to trade such a signal.