AC SUSCEPTIBILITY OF COBALT IN MERCURY MAGNETIC FLUIDS

The temperature dependence of the frequency-dependent magnetic suscept ibility chi' has been measured for tin-coated cobalt particles dispers ed in mercury, in the temperature range 80-290 K and for a driving fre quency of 10 kHz. A rounded maximum in chi' was observed at certain te mperature below the melting point of the mercury T(m). For T > T(m), a rapid increase of chi' with temperature is observed. This maximum dis appeared for the heat-treated sample. The results show that chi'(T) fo llows a Curie-Weiss behavior for T(B) < T < T(m), with positive orderi ng temperatures for the three samples. The results were analyzed withi n the context of Neel theory of superparamagnetism.