Short-range ferromagnetic order and metal-insulator transition in amorphous RexSi1 − x (Re = Gd, Tb, Y) nano-composites

The theoretical description and numerical calculations are presented for different a-RexSi1 − x (Re = Gd, Tb, Y, 0.1 < x < 0.15) alloys, with particular emphasis given to GdxSi1 − x. We took into account the strong topological disorder in the system, which causes the appearance of regions with high electron concentration (drops) around Re nano-clusters. We calculated the local density of electron states inside and outside the drops and established the criterion for their local instability towards ferromagnetic ordering. In the framework of the “local phase transition” approach, we demonstrated that short-range ferromagnetic order in Re nano-clusters exists in a wide range of temperatures and is more favorable inside the drops than in the matrix. We analyzed measurements of the temperature dependence of the electrical conductivity in a-RexSi1 − x and showed that the spin polarizations of electron states in the drops enhances the tendency towards the metal-insulator transition.