Critical behavior of amorphous ferromagnetic alloys

The results of our systematic magnetization and electrical resistivity measurements on amorphous transition metal-metalloid alloys are reviewed. In the real critical region, the amorphous ferromagnetic alloys (with composition well above the percolation threshold) and crystalline ferromagnets are found to behave alike but outside this temperature region, they exhibit a completely different behavior. These observations are discussed in the light of existing theories and shown to provide a straightforward explanation for a large scatter in the exponent values of glassy ferromagnets found in the literature. For Ni-rich Fe-Ni based glasses, only a small fraction of spins participates in the order-disorder transition. This finding is shown to have an important bearing on the nature of phase transitions in the spin systems with quenched disorder. We present a simple model for the peculiarities observed in the critical behavior of amorphous ferromagnets.