CLUSTER SPIN-GLASS MODEL FOR AMORPHOUS FE-ZR ALLOYS NEAR THE CRITICAL CONCENTRATION - A MAGNETIZATION STUDY

The magnetic properties of melt-quenched amorphous Fe100-xZrx (x = 7-12) alloys were studied in the temperature and magnetic field ranges 15 K < T < 300 K and 0 < H(ext) < 1.8 T, respectively. Assuming that Fc93Zr7 is an assembly of magnetic clusters with a blocking temperature distribution, the magnetization versus magnetic field curves were fitted using Neel's theory for fine particles at several temperatures in order to obtain the evolution of cluster parameters with temperature. The same model is used for Fe92Zrs and Fe88Zr12 above the Curie temperature (T(C)). When Neel's theory is modified to account for the interaction between the cluster moments, the experimental data are properly described by this frame. This model can explain both the low-temperature anomalies of susceptibility observed for x = 7-10 and the high-temperature superparamagnetic behaviour which is shown to be a characteristic feature of the whole a-Fe100-xZrx alloy series. The evolution of magnetic cluster behaviour with temperature and concentration is discussed.