The spin-glass behaviour of amorphous FexY100-x alloys (70<or=x<or=90) has been investigated by means of differential magnetic susceptibility dM/dH. In low magnetic fields, the dM/dH versus T curves show the peaks, indicating that the spin-glass state occurs through two steps. Two freezing temperatures are defined from the two peaks in the curve, i.e. the higher temperature is Tg and the lower temperature is Tf. From the results of the magnetization measurement as a function of temperature, i.e. the M versus T curve, it is indicated that the magnetization starts to decrease at Tg and a thermal irreversibility appears below T f with decreasing temperature. With increase in the applied magnetic field, a third peak appears at around 150 K in the dM/dH versus T curve for amorphous Fe84Y16 alloy. The position of this peak corresponds to the upper inflection point in the M versus T curve, being defined as the Curie temperature TC. Therefore, re-entrant behaviour appears in this system on application of a magnetic field. The concentration dependences of TC and Tf for a field of 500 Oe are very similar to those obtained in zero field for other amorphous Fe-RE alloys (RE: rare-earth metal) such as Fe-Lu and Fe-Ce systems.
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