DOPED MAGNETIC MOMENTS IN A DISORDERED ELECTRON SYSTEM: INSULATOR–METAL TRANSITION, SPIN GLASS AND "COLOSSAL MAGNETORESISTANCE"

Abstract

Recent experiments on the amorphous magnetic semiconductor Gd x Si 1-x, have revealed an insulator–metal transition (IMT), as a function of doping and magnetic field, a spin glass state at low temperature, and colossal magnetoresistance close to the IMT. There are also signatures of strong electron–electron interaction close to the IMT. Motivated by these results we examine the role of doped magnetic moments in a strongly disordered electron system. In this paper we study a model of electrons coupled to structural disorder and (classical) magnetic moments, through an essentially exact combination of spin Monte Carlo and fermion exact diagonalisation. Our preliminary results, ignoring electron–electron interactions, highlights the interplay of structural and magnetic "disorder" which is primarily responsible for the observed features in magnetism and transport.