Ab Initio Investigation of Crystalline and Amorphous GeTe Doped with Magnetic Impurities

Phase-change materials have important applications in the field of data storage. Recent experiments have shown that the prototypical phase-change materials GeTe and Ge2Sb2Te5 exhibit interesting magnetic properties when they are doped with transition metal elements, such as Cr, Mn and Fe. Here we report on first-principles studies of the structural and magnetic properties of amorphous and crystalline GeTe doped with Cr and Mn impurities. We employ large models containing 216 atoms. We set the impurity concentration to 2.7% and we assume ferromagnetic configurations. We show that Cr and Mn occupy substitutional Ge sites and display robust magnetic moments in the crystalline phase. In the amorphous phase, the impurities do not affect strongly the structure of the network. Interestingly, both Cr- and Mn-doped GeTe exhibit a significant magnetic contrast between the two phases, which originates from a decrease in the magnitude of the magnetic moments in the amorphous state.