Coexistence of incommensurate and commensurate spiral orders and pressure effect on polycrystalline CoCr2O4

In this paper, we have investigated the magnetism of multiferroic CoCr2O4. With decreasing temperature, CoCr2O4 first undergoes a ferrimagnetic transition at T-C then a long-range spiral spin transition at T-S followed by a magnetic lock-in transition at T-L. Coercive force manifests different slopes in different magnetic phases. Upon cooling the sample at 100 Oe to 5 K then warming back, the magnetization displays irreversibility between the cooling and warming sequence at temperatures below T-L. The irreversible behavior under the thermal-cycling is inert to magnetic field up to 45 kOe, indicating the coexistence of incommensurate and commensurate spiral orders. Both T-S and T-L are increased with the application of high pressure, which implies that the magnetic frustration is enhanced upon the shrinkage of lattice. The spin-lattice coupling is also revealed by infrared spectrum. (C) 2013 American Institute of Physics.