structural phase transition from cubic Fd¯ 3m to tetragonal I41/amd symmetry with c/a >1 is observed at TS = 16K in spinel GeCo2O4 below the N´eel temperature TN =21K. Structural and magnetic ordering appear to be decoupled with the structural distortion occurring at 16K while magnetic order occurs at 21K as determined by magnetic susceptibility and heat capacitymeasurements. 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 ≈8K. Magnetometry experiments reveal in GeFe2O4 a second antiferromagnetic transition, with TN1 = 7.9K and TN2 = 6.2K, that was previously unknown, and that bear a similarity to the magnetism of GeNi2O4.
Here, we study the low temperature tetragonal structural distortion of the spinel GeCo2O4. We find that the structural distortion is decoupled from antiferromagnetic ordering, occurring at TD =16K rather than at the N´eel temperature of 21K. We resolve the low-temperature nuclear structure of GeCo2O4 by Rietveld refinement of high resolution synchrotron x-ray diffraction data using a tetragonal I41/amd model with c/a > 1. The evolution of structure shows an elongation of CoO6 octahedra in the tetragonal phase of GeCo2O4. We discuss the mechanisms behind the structural distortion of GeCo2O4 in the context of known structural distortions in magnetic spinels.
to download the article click on the link below:
0 Comments