Tuning of multiferroic order with Co doping in $CuCr_{2}O_{4}$ : Interplay between structure and orbital order

Physical review materials 3(10), 104403-1-104403-9 (2019). doi:10.1103/PhysRevMaterials.3.104403
We observe a ferroelectric (FE) order in an unexplored CuCr2O4 with a reasonably high value of the FE Curie temperature (TFE) at 170 K, which is also much higher than the magnetic ordering temperature. The systematic substitution of Jahn-Teller (J-T) active divalent Cu ion by a non-Jahn-Teller active divalent Co ion causes a systematic shift of TFE from 170 K for x=0 to 146 K for x=0.8 in Cu1−xCoxCr2O4. The values of electric polarization vary from 0.0665 μCcm−2 to 0.1704 μCcm−2, which is maximum for x=0.6, associated with the highest value of the coercivity. The synchrotron diffraction studies of the compounds with x=0.2 and 0.8 confirm that a structural transition to a polar Ima2 space group from the tetragonally distorted I41/amd structure gives rise to the ferroelectricity. In all the members of Cu1−xCoxCr2O4 series, the TFE is observed at much higher temperature than the corresponding magnetic ordering temperatures (TN). These results are in contrast to that of the reported results of TFE
Published by APS, College Park, MD