Structural modulation induced by the incommensurate antiferromagnetic phase transition in ZnCr2Se4

Abstract

The structural properties of normal-type spinel ZnCr2Se4 have been studied as a function of temperature by means of X-ray diffraction using synchrotron radiation. It is found that a structural phase transition from cubic to orthorhombic symmetry occurs at 22.5 K (T-c). It is also found that, below T-c, Se ions are cooperatively displaced in a pseudo-tetragonal (001) plane. Since the Cr3+ ion has no orbital angular momentum, a CrSe6 octahedron is not distorted by a crystal field produced by surrounding Se2- anions. It is interpreted that the pseudo-tetragonal displacements of Se ions are induced by magnetostriction among Cr3+ ions in CrSe2 chains, in which Cr ions share two Se2- with each other along <110>.