Synthesis, crystal structure, magnetic properties and spin glass behaviour of the new ternary compound Cr_4TiSe_8

摘要

The new ternary selenide Cr_4TiSe_8 crystallises in the V_5S_8 type structure. The determination of the metal atom distribution over the three crystallographically independent sites using neutron scattering experiments reveals that the Ti atoms exclusively occupy the sites within the full metal atom layers with a pronounced preference for one of the two possible sites. The magnetic properties in the high temperature region exhibit Curie-Weiss behaviour with a paramagnetic Curie temperature #theta# of -300(5) K indicating strong antiferromagnetic exchange interactions. Between about 100 and 300 K the susceptibility data pass a very broad maximum and a qualitatively explanation is presented that base on antiferromagnetic exchange interactions between Cr atoms forming linear trimers, dimers, or Cr atoms being isolated. Below about 50 K the zero field cooled and field cooled susceptibility curves diverge suggesting spin glass behaviour. In the low temperature neutron diffraction patterns no additional peaks are observed which gives further evidence for the occurrence of a spin glass. Below 120 K the background of the diffraction patterns becomes modulated due to the short range magnetic interactions with sizes of the domains ranging from about 15 to 38 A. Low temperature single crystal X-ray investigations show a remarkable change of the contraction of the lattice parameters below about 220 K that may be due to the onset of the strong magnetic exchange interactions.