The effects of thermal spin fluctuation on the magnetic properties and its concentration dependence are investigated for ferromagnetic amorphous YNi alloys. The T 4 3 dependence of the square of the magnetization M2 is observed in amorphous Y12Ni88 and Y14Ni86 alloys. The validity of this relation becomes poor as the Ni concentration increases. Spontaneous volume magnetostriction μs is observed in these alloys. The value of μs becomes larger with increasing Ni concentration, indicating an increase in the spin fluctuation. The amplitude of the local spin-density fluctuation for amorphous Y10Ni90 alloy saturates after a linear increase above the Curie temperature TC. The inverse magnetic susceptibility for amorphous Y10Ni90 alloy follows the Curie-Weiss law above TC and shows a change in the slope at the temperature corresponding to the saturation of the amplitude.
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