Abstract
The magnetic behaviour of very fine nickel particles, chemisorbed on a silica carrier, has been studied using susceptibility measurements in small ac magnetic fields (≦0.8 Am−1). A detailed description of the simple ac susceptibility measuring procedure is given, which provides an excellent sensitivity. The temperature ranged from 4.2 K to 700 K. The application of an external magnetic dc field (0≦H ext≦6×104 Am−1) to the sample reduces the temperatureT max where the initial susceptibility has a maximum whereas the peak becomes broader and weaker. Additionally, the measurements determine the shift of the Curie temperatureT c′ which depends on the mean grain size. We discuss the particle interaction in terms of a mean field-like theory. However, as we found some discrepancies between our results and present theories, it appears that a percolation theory would be more appropriate to achieve a better understanding of the complicated interaction phenomena.
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