INITIAL SUSCEPTIBILITY OF IRON IN MERCURY MAGNETIC FLUIDS

Detailed studied of low-field susceptibility chi-(T), for fine tin-coated iron particles of median diameter almost-equal-to 40 angstrom dispersed in mercury were undertaken in the temperature range 65-400 K. Three samples with volume packing fractions epsilon = 0.01, 0.003 and 0.001, were prepared by electrodeposition. The samples were frozen successively in magnetic fields of 0, 160, 240 and 320 Oe. Our results show that chi-(T) exhibit three maxima for all studied samples and for all cooling fields. The first maximum was observed at certain characteristic temperatures, T(SG) below the melting point of mercury. The position of this maximum was found to depend strongly on both the intensity of cooling-fields and the iron particle concentrations. The second was observed at the melting point of mercury, T(m). The third was observed above the melting point of mercury, T(b), this was also found to depend on the iron concentration and on the intensity of the cooling field. The results show that chi-(T) follow a Curie-Weiss behaviour for T > T(b), with positive ordering temperatures. The value of the ordering temperature increases rapidly with increasing iron concentrations.