The magnetic structures of TlxCr5Se8 (x=1 and 0.2) as determined by neutron scattering

Abstract

The magnetic structures of TlCr5Se8 and Tl0.2Cr5Se8 were determined at 2 K using neutron scattering experiments. In the antiferromagnetic state the stoichiometric sample shows monoclinic symmetry with the magnetic cell exhibiting a doubling of the c-axis. All Cr atoms have magnetic moments in the b direction with magnitudes in accordance with Cr(III). As a consequence of direct and indirect superexchange, antiferromagnetic as well as ferromagnetic links between the different Cr atoms are observed. In Tl0.2Cr5Se8 in the antiferromagnetic state the symmetry is still monoclinic also showing a doubled c-axis. The Cr atoms have magnetic moments in the a–c-plane. Drastic changes of the Cr–Cr interatomic distances lead to a spin structure being significantly different from that observed for the stoichiometric sample. At about 70 K additional magnetic reflections which are due to the occurrence of an intermediate magnetic phase are observed in the powder pattern. The transition between the antiferromagnetic and the intermediate phase is accompanied by abrupt changes of the lattice parameters.