Synthesis, crystal structure, magnetic properties and spin glass behaviourof the new ternary compound Cr4TiSe8

The new ternary selenide Cr4TiSe8 crystallises in the V5S8 type structure. The determination of the metal atom distribution over the three crystallogr aphically independent sites using neutron scattering experiments reveals th at the Ti atoms exclusively occupy the sites within the full metal atom lay ers with a pronounced preference for one of the two possible sites. The mag netic proper-ties in the high temperature region exhibit Curie-Weiss behavi our with a paramagnetic Curie temperature theta of -300(5) K indicating str ong antiferromagnetic exchange interactions. Between, about 100 and 300 K t he susceptibility data pass a very broad maximum and a qualitatively explan ation is presented that base on antiferromagnetic exchange interactions bet ween Cr atoms forming linear trimers, dimers, or Cr atoms being isolated. B elow about 50 K the zero field cooled and field cooled susceptibility curve s diverge suggesting spin glass behaviour. In the low temperature neutron d iffraction patterns no additional peaks are observed which gives further ev idence for the occurrence of a spin glass. Below 120 K the background of th e diffraction patterns becomes modulated due to the short range magnetic in teractions with sizes of the domains ranging from about 15 to 38 Angstrom. Low temperature single crystal X-ray investigations show a remarkable chang e of the contraction of the lattice parameters below about 220 K that may b e due to the onset of the strong magnetic exchange interactions. (C) 2001 E ditions scientifiques et medicales Elsevier SAS. All rights reserved.