Abstract:
Mn
3O
4 and Mn
1.8Cr
1.2O
4 single-phase polycrystalline samples were successfully prepared by the conventional solid-phase method in order to investigate the effect of Cr
3+ doping on the magnetoelectric effect of the Mn
3O
4 system. The results from Rietveld refinement of powder X-ray diffraction patterns show a change in crystal structure after Cr
3+ doped Mn
3O
4, from a tetragonal (space group I4
1/amd \textI\text4_\text1\text/amd \textI\text4_\text1\text/amd ) to a cubic (space group \textFd\bar\text3\textm ) crystal system. Field emission scanning electron microscopy results indicate that the morphology of Mn
3O
4 is with a tight mosaic structure, while Mn
1.8Cr
1.2O
4 manifests as discrete pentahedron-like and octahedron-like. Moreover, the grain size of Mn
1.8Cr
1.2O
4 is about 1/8 times of that of the Mn
3O
4. Magnetization measurements show that the Yafet-Kittel type ferrimagnetic phase transition temperature increases from 43 K to 60 K after Cr
3+ doping, which is due to the enhancement of the magnetic interaction from the decrease of the Mn
3+(Cr
3+)/Mn
2+−O bond length and the increase of the Mn
3+(Cr
3+)−O−Mn
3+(Cr
3+) bond angle. In addition, the coercivity of Mn
1.8Cr
1.2O
4 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 Mn
3O
4 and Mn
1.8Cr
1.2O
4 near the magnetic phase transition temperature, and the dielectric anomaly peak positions don´t shift with frequency, indicating that the systems exist ferroelectric polarization related to the magnetic order, which originates from the nonlinear magnetic structure of the system.