High-field magnetization studies on an amorphous alloy with para, ferro and spin-glass regions

Recently, in the concentration-temperature plane, a number of amorphous alloys have been shown to exhibit para, ferro, and spin-glass regions with decreasing temperatures. In order to gain further insight into the role of competing interactions and the local anisotropy that may bring about spin-freezing at low temperatures, we have carried out high-field magnetization studies (in fields up to 160 kOe) between 4 and 120 K on an amorphous Fe ₁₅Ni₆₀P_{1 6}B₆Al₃ alloy. These results can be summarized as follows: 1) At all temperatures the magnetization does not saturate even at applied fields of 160 kOe; 2) For fixed field, the high field magnetization slowly decreases with temperature. To analyze these data, we first reanalyze earlier, low field data on this system to show that this material behaves in a way consistent with the prediction by Toulouse of a finite field, Ehrenfest second order transition to a mixed spin-glass-ferromagnetic phase as the temperature is reduced. This new analysis then suggests that the high field data is all taken in the paramagnetic phase, lying above this line of phase transitions. In this region, we develop a simple spin wave theory which accounts for points 1) and 2) in the high field data.