Weak itinerant ferromagnetism in amorphous M₉₀Zr₁₀ (M=Fe,Co,Ni) alloys

Abstract

Results of the magnetization measurements performed in the temperature range 4.2-300 K in fields up to 15 kOe on amorphous Fe₉₀Zr₁₀, Co₉₀Zr₁₀, and Ni₉₀Zr₁₀ alloys, prepared by the single-roller-quenching technique, are presented. While the glassy Co₉₀Zr₁₀ and Ni₉₀Zr₁₀ alloys at low fields show a normal ferromagnetic behavior down to 4.2 K, amorphous Fe₉₀Zr₁₀ exhibits a transition from the ferromagnetic state to the mictomagnetic state at a temperature Tf which lies well below the ferromagnetic ordering temperature. T_f decreases linearly with increasing H up to fields H-250 Oe and this linear dependence on H gives T_f(H=0)=40± 1 K. The magnetic behavior at high fields and the temperature dependence of spontaneous magnetization can be satisfactorily accounted for in terms of a theory proposed for weak itinerant ferromagnets. The unusually large value of the high-field susceptibility at 4.2 K observed for Fe₉₀Zr₁₀, in particular, is found to contain, besides the contribution arising due to the Invar characteristics of this alloy, a contribution typical of that observed in mictomagnetic alloys. Finally, from an appraisal of the present results and those previously reported on glassy Fe₉₀Zr₁₀, it is concluded that this alloy contains two types of magnetic electrons: those possessing itinerant character and giving rise to ferromagnetism (single-particle contribution) and Invar anomalies, and those having localized nature and responsible for both the ferromagnetic (spin-wave contribution) and the mictomagnetic behavior.