Structural modulation induced by the incommensurate antiferromagnetic phase transitionin ZnCr₂Se₄

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〉.

Structure and magnetism in the bond-frustrated spinelZnCr2Se4

“…1(a), confirmed a distortion to a subgroup of Fd3m. Attempts to refine the data in an orthorhombic symmetry including the recently proposed Fddd symmetry [37,38] or other tetragonal symmetries led to poorer fits. A summary of the key tetragonal models is provided in Table I U eq Cr (Å 2 ) 0.0059(2) 0.0061(2) 0.0067(7)…”

Structural transition in the magnetoelectricZnCr2Se4spinel under pressure

“…Previous studies at ambient pressure show that ZnCr 2 Se 4 undergoes a coupled magneto-structural transition below ~20 K [17][18][19][20][21][22] , whereas another structural transformation of the cubic structure into an unknown phase occurs at high temperatures 23 . Given this structural instability with varying temperature along with the strong spin-lattice coupling active in this system, the application of external pressure presents an appealing variable for further exploring and tuning the physical properties of this compound.…”

Structural modulation of spinel ZnCr2Se4 in the vicinity of antiferromagnetic phase transition induced by an applied magnetic field

“…In the present investigations, the notations (x, x, x), (x, x, z), and (x, y, z) refer to all atomic coordinates of equivalent positions in a structural unit cell. The x-value in the Fd3m structure was refined by a Rietveld analysis to neutron powder diffraction patterns of ZnCr 2 Se 4 taken at 2.5 K, though the structure is the orthorhombic symmetry Fddd [21]. We got the partial relative structure factors of F 222 (Se) and F 222 (Cr) to be about -95 and 48, respectively, where Cr ions occupy the special coordinates (1/2, 1/2, 1/2) in the Fddd structure.…”

“…More recently, it was found from neutron diffraction using a crystal [20] that the structural phase transition (T C ) from the cubic to orthorhombic symmetry simultaneously occurs at the antiferromagnetic phase transition temperature (T N ≈ 21 K), where the cubic and orthorhombic symmetry was 7 O h -Fd3m and 24 D 2h -Fddd, respectively. The structural phase transition results from pseudotetragonal displacements of Se ions, which is induced by magnetostriction [20,21]. In the present investigations, we try to study magnetic and structural modulations in the vicinity of the phase transitions of ZnCr 2 Se 4 as functions of applied magnetic field and temperature.…”