| Magnetic materials, magnetic refrigeration materials and magnetoelectricity, as a multifunctional materials, is of great research value and application prospect. Has been a hot area to exploring and developing function materials in condensed matter physics and material science system. Complex magnetic phase transitions of RFeO3, anisotropy magnetic entropy of ErFeO3 and the mutual regulation between magnetism and ferroelectricity, make RCrO3, RFeO3 and A4B2O9 has been widely concerned. Our works are explore the magnetism of CeCrO3, the magnetism and magnetic refrigeration of the TbFeO3 single crystal and the magnetoelectricity of the A4B2O9 system. This paper consists of six chapters and the main contents are as follows:In chapters one, we summarized the magnetism of RCrO3, the magnetic refrigeration of RFeO3 and the magnetoelectricity of A4B2O9 system. And introduce the research purpose and significance of this paper, as well as the main research content.In chapter two, we introduced the main experimental methods and the theoretical foundation in this thesis, including the preparation of sample, the structure analysis, and physical property measurement.In chapter three, we successfully synthesized the polycrystalline CeCrO3 with a single-phase orthorhombic perovskite structure. The magnetization compensation(for ZFC and FC under low fields) of CeCrO3 at 133 K is attributed to the antiparallel coupling between Ce3+ and Cr3+ moments, while the magnetization reversal starting from 43 K for H=1.2 k Oe is due to the spin flip caused by Zeeman energy between the net moments and the applied field. The temperature dependent spin flip transition is sensitive to the external field and provides an easy and predictable way to manipulate magnetism by changing the magnetic field.In chapter four, we have synthesized the single crystal TbFeO3 with a single-phase perovskite structure by optical floating zone method. M-T curves and isothermal M-H curves indicate that a strong interaction between 3d and 4f electrons drives important changes of spin configuration that is highly sensitive to applied magnetic field and temperature. Furthermore, TbFeO3 presents a giant rotating field entropy change between a, b and c axes(even larger than previous reports) that may find potential uses in magnetic refrigeration by simply rotating the sample.In chapter five, we have synthesized the single crystal Co4Nb2O9, Mn4Nb2O9 and Co4Ta2O9 with a single-phase corundum-type structure by the optical floating zone method. For Co4Nb2O9, we realize the interaction between electricity and magnetism. And give it’s magnetic structure by neutron diffraction. Co4Nb2O9 shows a large nonlinear magnetoelectric effect which may find potential application in multiferroic devices. For Mn4Nb2O9,different from Co4Nb2O9, an antiferromagnetic transition is found at Néel temperature TN=107 K along c axis and the spin flop wasn’t occurred until the magnetic field up to 70 kOe. There is a temperature induced structure phase transition around Néel temperature. We believe the antiferromagnetic transition is caused by the structure phase transition. Co4Ta2O9 shows similar behaviour to Co4Nb2O9. There is a critical Zeeman energy to driven spin flop. The critical Zeeman energy of Co4Ta2O9 is smaller than that of Co4Nb2O9. This make Co4Ta2O9 more easier to be used.In chapter six, we summarized the research work of this thesis. we pointed out the extensive potential application and perspective of the CeCrO3 polycrystalline, TbFeO3 single crystal and A4B2O9 single crystal. |
PDF Full Text Request