Structural modulation induced by the incommensurate antiferromagnetic phase transitionin ZnCr₂Se₄

Abstract

Abstract The structural properties of normal‐type spinel ZnCr 2 Se 4 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 Cr 3+ ion has no orbital angular momentum, a CrSe 6 octahedron is not distorted by a crystal field produced by surrounding Se 2– anions. It is interpreted that the pseudo‐tetragonal displacements of Se ions are induced by magnetostriction among Cr 3+ ions in CrSe 2 chains, in which Cr ions share two Se 2– with each other along 〈110〉.