A neutron powder diffraction study of the helimagnetic structure of TlCo 2 Se 2− x S x

• Published in: Journal of magnetism and magnetic materials 2010, Vol.322 (6), p.681
• Main Authors: Ronneteg, Sabina, Berger, Rolf, André, G.
• Format: Article
• Language: English
• Subjects: Chemistry; Inorganic chemistry; Kemi; NATURAL SCIENCES; NATURVETENSKAP; Oorganisk kemi
• ISSN: 1873-4766; 0304-8853
• DOI: 10.1016/j.jmmm.2009.10.040

The magneti clayer structure of TlCo2Se2-xSx has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged with in the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo2Se2 form a helix along the c-axis with a turning-angle of similar to 119 degrees at 1.4 K. This kind of helical structure prevails for 0 <= x <= 1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34 degrees, showing an almost linear relationship with the interlayer distance of Co-Co. For x >= 1.75 the interlayer couplingchanges to ferromagnetic. Unexpectedly, two helices were found to coexist at x = 0.5 and x = 1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106 degrees, resp., 73 degrees) together with a commensurate angle of 90 degrees. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites.