Effects of Cr3+doping on the structure,morphology,magnetic and dielectric properties of Mn3O4
Mn3O4 and Mn1.8Cr1.2O4 single-phase polycrystalline samples were successfully prepared by the conventional solid-phase method in order to investigate the effect of Cr3+doping on the magnetoelectric effect of the Mn3O4 system.The results from Rietveld refinement of powder X-ray diffraction patterns show a change in crystal structure after Cr3+doped Mn3O4,from a tetragonal(space group I41/amdI41/amdI41/amd)to a cubic(space group Fd(3)m)crystal system.Field emission scanning electron microscopy re-sults indicate that the morphology of Mn3O4 is with a tight mosaic structure,while Mn1.8Cr1.2O4 manifests as discrete pentahedron-like and octahedron-like.Moreover,the grain size of Mn1.8Cr1.2O4 is about 1/8 times of that of the Mn3O4.Magnetization measure-ments show that the Yafet-Kittel type ferrimagnetic phase transition temperature increases from 43 K to 60 K after Cr3 doping,which is due to the enhancement of the magnetic interaction from the decrease of the Mn3+(Cr3)/Mn-O bond length and the in-crease of the Mn3+(Cr3+)-O-Mn3+(Cr3+)bond angle.In addition,the coercivity of Mn1.8Cr1.2O4 decreases significantly,which can be understood in terms of the reduction in force between crystalline grains.The dielectric effect study shows that the dielectric anomaly peaks are observed in Mn3O4 and Mn1.8Cr1.2O4 near the magnetic phase transition temperature,and the dielectric anomaly peak posi-tions don't shift with frequency,indicating that the systems exist ferroelectric polarization related to the magnetic order,which origi-nates from the nonlinear magnetic structure of the system.
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