Thermal demagnetization due to spin-wave and Stoner single-particle excitations in amorphous Co₉₀Zr₁₀ alloy

Abstract

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) are nothing but a set of parallel straight lines at high fields (H>or approximately=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< or approximately=0.1 T_c whereas Stoner single-particle excitations are mainly responsible for the decline of M(0,T) with increasing temperature for T>or approximately=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 approximately=0.24 meV AA² K^-1 typical of Co-based amorphous alloys; and (iv) Stoner's criterion IN(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.