THERMAL DEMAGNETIZATION DUE TO SPIN-WAVE AND STONER SINGLE-PARTICLE EXCITATIONS IN AMORPHOUS CO90ZR10 ALLOY

Results of the high-precision magnetization (M) measurements performed on amorphous Co90Zr10 alloy at temperatures (T) ranging from 4.2 to 300 K in external magnetic fields (H) up to 15 kOe are presented. At low temperatures, magnetization does not saturate even at the highest field H = 15 kOe and the high-field differential susceptibility, chi-hf(0), is larger by an order of magnitude in the alloy in question than in crystalline Co. M2(H, T) versus H/M(H, T) isotherms (Arrott plot isotherms) am nothing but a set of parallel straight lines at high fields (H greater than or similar to 3 kOe) over the temperature range investigated. An elaborate analysis of the 'in-field', M(H,T), as well as 'zero-field' (spontaneous), M(0, T), magnetization data reveals that: (i) spin-wave excitations give a dominant contribution to thermal demagnetization of M(0, T) for T less than or similar to 0.1 T(c) whereas Stoner single-particle excitations are mainly responsible for the decline of M(0, T) with increasing temperature for T greater than or similar to 0.1 T(c); (ii) the particle-hole pair excitations are very weakly correlated; (iii) the spin-wave stiffness coefficient, D, is independent of H, renormalizes with temperature in accordance with the expression predicted by the itinerant-electron model and the D/T(c) ratio possesses a value congruent-to 0.24 mev angstrom2 K-1 typical of Co-based amorphous alloys; and (iv) Stoner's criterion I N(E(F)) > 1 for the occurrence of ferromagnetism is satisfied. The unusually large value of chi-hf(0), linear Arrott plot isotherms at high fields and the above features (i)-(iv) of the magnetization data find a straightforward explanation in terms of a theory proposed for weak itinerant ferromagnets.