Crystal structures, unusual magnetic properties and electronic band structures of Cr5-xTIxTe8

The effect of substitution of the cation Cr by Ti in Cr5Te8 has been investigated with respect to its crystal structure, magnetic properties, and electronic structure. The compounds Cr5-xTixTe8 (x = 0, 0.5, 1, 1.5, 1.85, 2, 3, 4, 5) were synthesized at elevated temperatures followed by slow cooling the samples to room temperature. The crystal structures have been refined with X-ray powder diffraction data with the Rietveld method. Three structural modifications are identified: monoclinic with space group F2/m for Cr5-xTixTe8 (x = 0, 0.5, 1, 1.5, 1.85), trigonal supercell with space group P-3m1 for Cr5-xTixTe8 (x = 2, 3), and trigonal basic cell with space group P-3m1 for Cr5-xTixTe8 (x = 4, 5). The structures of all these phases are related to the NiAs structure with full and deficient metal layers stacking alternatively along the c-axis. The irreversibility in the field-cooled/zero-field-cooled magnetization with low field depends strongly on the Ti concentration x. Four types of magnetic states are distinguished: re-entrant ferromagnet for m-Cr5Te8, cluster-glass for m-Cr4.5Ti0.5Te8 and m-Cr4TiTe8, antiferromagnetic for m-Cr3.5Ti1.5Te8, and spin-glass for tr-Cr3TiTe8, tr-Cr3Ti2Te8, and Cr0.25TiTe2. Accompanying spin polarized scalar-relativistic Korringa-Kohn-Rostoker band-structure calculations strongly support the observation that the crystallographic sites in the full metal layers are preferentially occupied and predict that Ti atoms have the preference to occupy the full metal layers. These compounds are predicted metallic. Results for the spin-resolved DOS and magnetic moments on each crystallographic sites are presented. (c) 2005 Elsevier Inc. All rights reserved.