Short-range ferromagnetism and transport properties of amorphous (Gd, Y)xSi1−x alloys

Abstract

We present a theoretical description and electrical conductivity measurements for amorphous (Gd, Y)xSi1−x alloys with 0.1 < x < 0.2. In our model, we take into account the strong topological disorder in the system, causing the appearance of regions with higher electron density (electron “ drops”) around nanoscale structural defects enriched with rare-earth ions (“clusters”). We calculate the local density of electron states in the drops and in the matrix and establish the criterion for local instability to ferromagnetism. In the framework of the “local phase transition” approach, we find that short-range ferromagnetic order is more favorable inside the drops than in the matrix and exists in a wide temperature range. We analyze recent measurements of the temperature and magnetic-field dependence of the electrical conductivity in these systems and show that the spin polarization of the electron states in the drops enhances the tendency towards the metal-insulator transition.