engleski

Magnetic excitations in very dilute amorphous Fe_xN_(80-x)B_18Si_2 ferromagnets

The magnetization of seven amorphous ferromagnetic alloys FexNi80-xB18Si2 with the magnetic atom concentrations x in the vicinity of the magnetic percolation threshold (x(c) congruent to 2.32 at% Fe) has been studied. Over a broad temperature range from 1.8 K to T-c of the respective alloy, the temperature dependence of the magnetization M(T) is well described for all alloys by using the effective density of states, N-eff(omega), of the magnetic excitations, which in the limit of low frequencies (omega much less than omega(c)) reflects the magnon density of states, whereas at high frequencies (omega much greater than omega(c)) represents the density of states of the short-wavelength (localized) fractons. The values derived for the spin-wave stiffness constants, D, and the crossover frequencies, omega(c), show a power-law dependence on the reduced concentration. Accordingly, the disappearance of the ferromagnetism with decreasing concentration x of magnetic atoms in the studied alloy system is well described in terms of the percolation theory.

magnetic excitations; disordered systems; percolation; fractals

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