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

The magnetic properties of melt-quenched amorphous Fe100-xZrx (x = 7-1 2) 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 Fc9 3Zr7 is an assembly of magnetic clusters with a blocking temperature d istribution, the magnetization versus magnetic field curves were fitte d using Neel's theory for fine particles at several temperatures in or der to obtain the evolution of cluster parameters with temperature. Th e same model is used for Fe92Zrs and Fe88Zr12 above the Curie temperat ure (T(C)). When Neel's theory is modified to account for the interact ion between the cluster moments, the experimental data are properly de scribed by this frame. This model can explain both the low-temperature anomalies of susceptibility observed for x = 7-10 and the high-temper ature superparamagnetic behaviour which is shown to be a characteristi c feature of the whole a-Fe100-xZrx alloy series. The evolution of mag netic cluster behaviour with temperature and concentration is discusse d.