Anion substitution effects on structure and magnetism in the chromium chalcogenide Cr5Te8 - Part I: Cluster glass behavior in trigonal Cr(1-x) Q(2) with basic cell (Q = Te, Se; Te : Se=7 : 1)

摘要

The effect of substitution of the anion Te by Se in non-stoichiometric Cr5Te8 has been investigated with respect to its crystal structure, magnetic properties, and electronic structure. The compounds Cr((1 + x))Q(2) (Q = Te, Se; Te:Se = 7:1; (1 + x) = 1.234(6), 1.264(6), 1.300(7)) were synthesized at elevated temperatures followed by quenching the samples to room temperature. The crystal structures have been refined with X-ray powder diffraction data with the Rietveld method in the trigonal space group P (3) over bar m1 with lattice parameters a = 3.8651(1)-3.8831(1) Angstrom and c = 5.9917(2)-6.0528(2) Angstrom. The structure is 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 suggests that the substitution effects of one Te by one Se is strong enough to cause cluster-glass behavior, from ferromagnetic Cr5Te8 to cluster-glass Cr((1 + x))Q(2). Non-saturation magnetizations at 5.5 T and the magnetic relaxation results further support the existence of cluster-glass behavior. Accompanying SPR-KKR (spin-polarized relativistic Korringa-Kohn-Rostoker) band structure calculations strongly support the observation that the Cr(1) sites are preferentially occupied by Cr atoms and predict that these compounds are metallic. Results for the spin-resolved DOS and magnetic moments on each crystallographic sites are presented. (C) 2004 Elsevier Inc. All rights reserved.