Spin-induced symmetry breaking in orbitally ordered NiCr2O4and CuCr2O

Matthew R. Suchomel

¹

,

Daniel P. Shoemaker

²

,

Lynn Ribaud

³

et al.

Abstract

At room temperature, the normal oxide spinels NiCr2O4 and CuCr2O4 are tetragonally distorted and crystallize in the I41/amd space group due to cooperative Jahn-Teller ordering driven by the orbital degeneracy of tetrahedral Ni 2+ (t 4 2 ) and Cu2 ). Upon cooling, these compounds undergo magnetic ordering transitions; interactions being somewhat frustrated for NiCr2O4 but not for CuCr2O4. We employ variable-temperature high-resolution synchrotron X-ray powder diffraction to establish that at the magnetic ordering temperatures there are further structural changes, which result in both compounds distorting to an orthorhombic structure consistent with the F ddd space group. NiCr2O4 exhibits additional distortion, likely within the same space group, at a yet-lower transition temperature of T = 30 K. The tetragonal to orthorhombic structural transition in these compounds appears to primarily involve changes in NiO4 and CuO4 tetrahedra.

Competing Jahn-Teller distortions and ferrimagnetic ordering in the geometrically frustrated systemNi1−xCuxCReehuis1, Tovar2, Többens3 et al. 2015Phys. Rev. B3710450View full textAdd to dashboardCite

“…22 At low temperature (10 K) both compounds showed an orthorhombic splitting, where the splitting of CuCr2O4 (c/a = 1.00087) was found to be less pronounced than that of NiCr2O4 (c/a = 1.00176). 22 In the present work we have investigated In this section we want to point out some systematic structural changes in the system Ni1xCuxCr2O4 at 2 K. Despite the fact that the end members NiCr2O4, and CuCr2O4 show an elongation (along c) and a flattening (along a) of the NiO4 and CuO4 tetrahedra, respectively, the crystal structures of both can be described in the orthorhombic space group Fddd. 22 Over the whole composition range of the system Ni1xCuxCr2O4 a continuous description is possible, where the a parameter is always the shortest one, and the c parameter always the largest (Table I).…”

“…22 In the present work we have investigated In this section we want to point out some systematic structural changes in the system Ni1xCuxCr2O4 at 2 K. Despite the fact that the end members NiCr2O4, and CuCr2O4 show an elongation (along c) and a flattening (along a) of the NiO4 and CuO4 tetrahedra, respectively, the crystal structures of both can be described in the orthorhombic space group Fddd. 22 Over the whole composition range of the system Ni1xCuxCr2O4 a continuous description is possible, where the a parameter is always the shortest one, and the c parameter always the largest (Table I). In accordance with the room temperature data ( Table I it can be seen that the strongest changes degrees with increasing copper content, whereas for 3 the changes are less than 0.7°.…”

Orthorhombic distortion and orbital order in the vanadium spinelFeV2O4

“…These refinements are best described by the orthorhombic model with the space group F ddd. This space group is a subgroup of the tetragonal space group I 4 1 /amd, and it has been often applied to describe structural ground states of the spinels with JT active ions located at the A site [23]. The characteristic atomic displacement (mentioned in Sec.…”

Magnetic and structural phase transitions in the spinel compoundFe1+xCr2−xMa1, Garlea2, Rondinone3 et al. 2014Phys. Rev. B

“…Previously, a largely separate line of research has been devoted to the spin-lattice interaction which is related to the spin frustration and the cooperative Jahn-Teller distortion especially for the compounds involving orbitally active Asite cations. 17,[20][21][22]27,[31][32][33][34][35] However, very few materials have been studied from the view point of the coupling between frustration and Jahn-Teller effects by changing the orbital configuration of B-site cation. ions.…”