Noncollinear magnetism in amorphous Fe-Y alloys

Abstract

Iron-rich amorphous alloys with nonmagnetic transition metals (TM) or rare-earth (RE) metals show a rich variety of complex spin-structures that have been described as spin-glass-like, spero- or asperomagnetic. Amorphous Fe-Y alloys have attracted particular attention because it has been suggested that, in contrast to other amorphous Fe-TM and Fe-RE alloys showing re-entrant spin-glass behaviour, in Fe-Y alloys the spin-glass transition could occur directly from the paramagnetic phase. It has also been suggested that, unlike most other alloys where the spin-glass-like phase is restricted to high Fe concentrations, amorphous Fe-Y alloys are noncollinear at all compositions. We have recently presented a technique for a selfconsistent calculation of noncollinear spin-structures in crystalline and amorphous alloys based on a tight-binding-Hubbard Hamiltonian generated via a canonical transformation of the local-spin-density (LSD) Hamiltonian. This approach has been used to analyze the magnetic properties of amorphous Fe-Y alloys. We show that, unlike, for example, amorphous Fe-Zr alloys where the net magnetization is well defined in the spin-glass and in the ferromagnetic phases and independent of the initialization of the magnetic structure, for Fe-Y energetically nearly degenerate low- and high-moment phases can be induced by different initializations. This could explain the observed strong dependence of the magnetic state on the preparation of the amorphous phase and its strong variation under applied external fields or pressures.