MAGNETIC EXCITATIONS IN FE3NI77B18SI2 AMORPHOUS ALLOY

The thermal demagnetization of Fe3Ni77B18Si2 amorphous ferromagnetic a lloy (T-c = 19.5 K) has been studied in the temperature range 5-30 K. The magnetization data M(T) are analysed by using the Bose-Einstein in tegration of the effective density of states which interpolates betwee n the long wavelength magnon (n(omega) alpha omega(d/2-1)) and the sho rt wavelength fracton (n(omega) alpha omega(<(d)over tilde /2-1>)) reg ime. The best fit yields the following parameters: the spin-wave stiff ness constant D = 2.72 meV Angstrom(2), the crossover frequency omega( c) = 1.94 x 10(10) s(-1) and the fracton dimension (d) over tilde = 1. 37. Therefore, our results confirm the contribution of the short wavel ength excitations in the process of thermal demagnetization of our all oy and support the Alexander-Orbach conjecture that (d) over tilde = 4 /3 for d greater than or equal to 2.