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 ${\mathrm{Fe}}_{90}$ ${\mathrm{Zr}}_{10}$, ${\mathrm{Co}}_{90}$ ${\mathrm{Zr}}_{10}$, and ${\mathrm{Ni}}_{90}$ ${\mathrm{Zr}}_{10}$ alloys, prepared by the single-roller-quenching technique, are presented. While the glassy ${\mathrm{Co}}_{90}$ ${\mathrm{Zr}}_{10}$ and ${\mathrm{Ni}}_{90}$ ${\mathrm{Zr}}_{10}$ alloys at low fields show a normal ferromagnetic behavior down to 4.2 K, amorphous ${\mathrm{Fe}}_{90}$ ${\mathrm{Zr}}_{10}$ exhibits a transition from the ferromagnetic state to the mictomagnetic state at a temperature $T_f$ which lies well below the ferromagnetic ordering temperature. $T_f$ decreases linearly with increasing $H$ up to fields $H\sim 250$ Oe and this linear dependence on $H$ gives $T_f\mathrm{}(H=0\mathrm{})=40\mathrm{}\pm 1$ 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 ${\mathrm{Fe}}_{90}$ ${\mathrm{Zr}}_{10}$, 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 ${\mathrm{Fe}}_{90}$ ${\mathrm{Zr}}_{10}$, 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.