Structural, electronic, and magnetic properties of Fe-Y alloys.

Abstract

Results of ab initio calculations of the structural, electronic, and magnetic properties of crystalline and amorphous Fe-Y alloys are presented. The structure of the amorphous phases is generated via a simulated molecular-dynamics quench, based on effective interatomic forces derived from tight-binding-bond theory. The results show that a pronounced chemical short-range order (preferred heterocoordination) exists at all compositions and that at short distances the local topology is similar in the crystalline and glassy phases. In the Y-rich alloys, medium-range concentration fluctuations are superposed to the local order. The investigation of the electronic structure using self-consistent spin-polarized linear muffin-tin orbital calculations confirms that the bonding properties are similar in the crystalline and amorphous phases. The crystalline compounds are ferrimagnetic, the negative Y moment is induced by a strong covalent interaction of the Y d band with the minority-spin Fe d band. Ferrimagnetism is also found in the amorphous alloys. In the Fe-rich range (more than 80 at. % Fe) competing ferro- and antiferromagnetic Fe-Fe exchange interactions lead to coexisting positive and negative Fe moments. The decrease of the magnetic moments of the Fe atoms with increasing Y content is strongly influenced by the strong coupling of the Fe spins to the Y moments---as a consequence a spontaneous Fe moment exists even at very small Fe-Fe coordination numbers. In addition the structural inhomogeneity of the Y-rich amorphous alloys leads to cluster magnetism.