Research On Thermal And Magnetic Properties Of Single Crystal SmTiO₃ At Low Temperature

In the perovskite Ti oxide RTiO₃ (where R represents the trivalent rare-earth ions), which is a typical Mott-Hubbard insulator. The titanates have the t2g bands at the Fermi level in contrast with the cuprates and manganites ,the manganites have the eg bands at the Fermi level similar to the cuprate superconductors, Titanate compounds have been recognized as key materials for understanding the coupling of magnetism and orbitals in strongly correlated electron systems. We have studied the low temperature specific heat, heat conductivity and magnetism for the single crystal of SmTiO₃ which locate at antiferromagnetic-to-ferromagnetic(AFM-FM) phase transition and reveal magnetism and orbital order magnetic field dependence as well as several kind of magnetic ion cooperations and competition effect in the magnetic field.First, we have studied the low temperature specific heat of single crystal sample SmTiO₃. As magnetic field increase, SmTiO₃ specific heat peak translates toward low temperature because magnetic field destroys the antiferromagnetic order arrangement .Schottky anomaly of SmTiO₃ specific heat is also shown at low temperature because the exchange field makes Sm³⁺ ion doubly degenerate level splitting. We have not found Schottky specific heat peak of NdTiO3, which can be attributed to the magnetic moment of Nd³⁺ ions perpendicular to the Ti³⁺ ion exchange field.Then, we exert a magnetic field on easy magnetization axis(c axis) of single crystal SmTiO₃, both sides of the ? specific heat peak appears abnormal. On the left side, magnetic field force the electrons virtual transite from t2g energy level to eg energy level and produce heat contribution, on the right side, the heat presents a new peak. Through the the heat conductivity research under magnetic field, we discover this peak comes from the orbital order. The magnetic field will cause the separation of orbital order and the spin order. However, other RTiO₃ do not have this feature. From the origin of spin order and orbital order of the RTiO₃, we reveal the reason for spin-orbital separation of SmTiO₃ in the magnetic field, SmTiO₃ locate at antiferromagnetic boundary in the AFM-FM phase boundary and Sm³⁺ ionic radius is close to . There exists almost the largest intrinsic local distortions of oxygen octahedra in the SmTiO₃. Intrinsic distortion of the octahedral will bias the orbital order and weaken spin-orbit coupling which is produced by the intrinsic spin-orbita superexchange interaction. These factors lead to the separation ? rR?? 1.110A? of orbital order and spin order in the magnetic field for SmTiO₃.At last, we study the magnetic properties of SmTiO₃ in different directions and discovered that'a'direction presents the magnetization reverse compared to the results of other experiments. This kind of magnetization reverse phenomenon is produced by the competition between single ion anisotropy and the paramagnetic Sm³⁺ ion under different temperature and magnetic field. Ferromagnetism appearing in the'b'directions comes from the tilt of the anti-ferromagnetic because of the D-M interaction below the TN temperature. Under the strong magnetic field,'c'directional M-H curve has been bended, which due to additional magnetic field disturbed the original anti-ferromagnetic. Then system's transformation temperature of magnetism is reduced and the paramagnetic emerge. that is consistent with the M-T curve of'c'direction. As the temperature decreased, high field M-T curve going up in'a'and'b'direction, which originated from paramagnetic Sm³⁺ ions in the system.