Structural distortion below the Néel temperature in spinel GeCo 2 O 4

摘要: A structural phase transition from cubic $Fd\overline{3}m$ to tetragonal $I4{}_{1}/amd$ symmetry with $c/ag 1$ is observed at ${T}_{S}=16$ K in spinel ${\mathrm{GeCo}}_{2}{\mathrm{O}}_{4}$ below the N\'eel temperature ${T}_{N}=21$ K. Structural and magnetic ordering appear be decoupled distortion occurring 16 while order occurs 21 as determined by susceptibility heat capacity measurements. An elongation of ${\mathrm{CoO}}_{6}$ octahedra ${\mathrm{GeCo}}_{2}{\mathrm{O}}_{4}$. We present complete crystallographic description space group discuss possible origin this context known transitions spinels. exhibits magnetodielectric coupling ${T}_{N}$. The related spinels ${\mathrm{GeFe}}_{2}{\mathrm{O}}_{4}$ ${\mathrm{GeNi}}_{2}{\mathrm{O}}_{4}$ have also been examined for comparison. were not detected either compound down $T\ensuremath{\approx}8$ Magnetometry experiments reveal a second antiferromagnetic transition, ${T}_{N1}=7.9$ ${T}_{N2}=6.2$ K, that was previously unknown bears similarity magnetism ${\mathrm{GeNi}}_{2}{\mathrm{O}}_{4}$.