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Percolation-like behaviour of the spin-wave stiffness in very dilute amorphus (Fe_pNi_1-p)_80B_18Si_2 ferromagnets

The thermal demagnetization of several (FepNi1-p)(80)B18Si2 amorphous ferromagnetic alloys has been analyzed in terms of the percolation model for very dilute ferromagnets. Taking into account the contributions from both the long wavelength magnons and short wavelength fractons we obtained the power law concentration dependence of the spin-wave stiffness in the vicinity of the critical concentration p(c), D(p) proportional to (p - p(c))(eta) with eta = 1.37. The ratio between the spin-wave stiffness and the Curie temperature, D(p)/T-c(p), also shows the power law variation with p. Since the corresponding exponent is positive this ratio vanishes as p tends to p(c).

spin dynamics; fractons; disordered systems

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