Structural distortion below the Néel temperature in spinelGeCo2O4

Abstract

A structural phase transition from cubic F d3m to tetragonal I41/amd symmetry with c/a > 1 is observed at TS = 16 K in spinel GeCo2O4 below the Néel temperature TN = 21 K. Structural and magnetic ordering appear to be decoupled with the structural distortion occurring at 16 K while magnetic order occurs at 21 K as determined by magnetic susceptibility and heat capacity measurements. An elongation of CoO6 octahedra is observed in the tetragonal phase of GeCo2O4. We present the complete crystallographic description of GeCo2O4 in the tetragonal I41/amd space group and discuss the possible origin of this distortion in the context of known structural transitions in magnetic spinels. GeCo2O4 exhibits magnetodielectric coupling below TN. The related spinels GeFe2O4 and GeNi2O4 have also been examined for comparison. Structural transitions were not detected in either compound down to T ≈ 8 K. Magnetometry experiments reveal in GeFe2O4 a second antiferromagnetic transition, with TN1 = 7.9 K and TN2 = 6.2 K, that was previously unknown, and that bear a similarity to the magnetism of GeNi2O4.

Hedgehog-lattice spin texture in classical Heisenberg antiferromagnets on the breathing pyrochlore lattice

“…In experiments, although various classes of breathing pyrochlore antiferromagnets such as the chromium oxides Li(Ga, In)Cr 4 O 8 [53, 59-66, 69, 70] and sulfides Li(Ga, In)Cr 4 S 8 [67,68,71] and the quantum magnet Ba 3 Yb 2 Zn 5 O 11 [72][73][74][75][76] have been studied, the ( 12 , 1 2 , 1 2 ) spin correlation has not been reported so far. On the other hand, the uniform pyrochlore antiferromagnets GeB 2 O 4 (B=Ni, Co, Fe, Cu) [77][78][79][80][81][82][83][84][85][86][87] do exhibit ( 12 , 1 2 , 1 2 ) magnetic LRO, although the experimentally proposed spin structure as well as the estimated exchange interactions (e.g., ferromagnetic J 1 ) seems to be different from the ones in the present theoretical model. If one can introduce the breathing alternation in the GeB 2 O 4 family, modifying the exchange interactions, the (…”

Up-up-down-down magnetic chain structure of the spin- 12 tetragonally distorted spinel GeCu2O4Zou1, Cai2, Garlea3 et al. 2016Phys. Rev. B234232View full textAdd to dashboardCite

“…: 3d 6 , S = 2) either, although the nature of its magnetic ground state remains enigmatic [16,20,21]. GeCu 2 O 4 (Cu…”

Field-driven magnetostructural transitions in GeCo2O4

“…This is at variance with GeCo 2 O 4 in which a unique magnetic transition is observed at T N =23.5 K. This is ascribed to a structural distortion that couples the two sites and allows to reduce the frustration in the absence of any external magnetic field. This distortion was proposed to be mainly cubic-to-tetragonal from powder neutron and X-ray diffraction [1,15].…”