SUPERPARAMAGNETISM IN MELT-SPUN CUCO GRANULAR SAMPLES

We have studied the magnetic properties of a melt-spun granular sample of Cu87Co13. The Cu matrix contains very fine particles of Co, having a bimodal distribution of sizes: 'larger' particles (similar to 300 A ngstrom) and very much smaller particles (< 15 Angstrom) with the latt er exhibiting superparamagnetism. The magnetisation data indicate a sp read of sizes for the smaller superparamagnetic particles, ranging fro m individual Co atoms up to clusters of more than 100 atoms of Co. Ass uming a simple distribution of particle sizes, we calculated the magne tic field dependence of the magnetisation of the superparamagnetic par ticles and find excellent agreement with experiment.