Study On Growth And Low Temperature Properties Of?Sm,Gd?TiO₃ Single Crystals

In the perovskite rare earth titanate RTiO₃ system,there is an orthorhombic distortion?GdFeO₃ type distortion?,and as the radius of the rare earth ions decreases,the degree of distortion of the GdFeO₃ type increases,and at the same time the order of the Ti³⁺ions spin transforms from antiferromagnetic?R=La,Pr,Nd,Sm?into ferromagnetic?R=Gd,...,Lu,Y?.This phenomenon is called magnetic order transition.The origin of the AFM-FM magnetic order transition and the microscopic physical image that occur in the RTiO₃ system with decreasing radius of the rare earth ions are still controversial.This article mainly studies the degree of distortion of the crystal lattice by allowing SmTiO₃and GdTiO₃ to form a solid solution.The thermal and magnetic properties of the sample are measured and the change law is analyzed.The anisotropy of the system is found and the source of the system is finally explained.The specific results are as follows:In this paper,the growth conditions by optical floating zone method of single crystals of this system were studied firstly,and?Gd,Sm?TiO₃ single crystals were grown.Secondly,specific heat tests on oriented single crystals under different magnetic field was conducted to study the anisotropy of the samples.In the specific heat test of Gd_0.2Sm_0.8TiO₃ samples,it has been found that the antiferromagnetic coupling of the c-axis is slightly stronger than that in the ab plane.This might be the d-type Jahn-Teller distortion and the GdFeO₃ type distortion mutuality competition increases the antiferromagnetic coupling in the c-axis direction.When a magnetic field was applied parallel to the c axis of Gd_0.3Sm_0.7TiO₃sample,the antiferromagnet was strongly suppressed by the magnetic field and finally disappeared.However,the specific heat peak of the vertical c axis remained.This reflected that the TiO₆ octahedron was continuously increased due to the increase of the Gd doping amount.The effect of the distortion of GdFeO₃ dominates.After increasing the doping amount,the anisotropy of Gd_0.4Sm_0.6TiO₃ almost disappeared.This is because when the Gd doping amount is relatively large,the antiferromagnetic interaction and the ferromagnetic interaction compete fiercely,and the magnetic moment tends to disorderly arrangement,ie the magnetic moment has no very favorable arrangement direction,so the anisotropy is weaker.Thermal conductivity tests have found that during the magnetic transition,the coupling between spin-spin,orbital-orbital,and spin-orbital decreases as the phase boundary is approached,but spin-orbit and orbital-The orbital interaction decays faster,and the interaction between spin and spin is relatively stronger,which ultimately leads to the separation of spin order and orbital order during the magnetic transition.Finally,the magnetization curves of the single crystals of this system was tested and it has been found that the samples of Gd_0.3Sm_0.7TiO₃ exhibited relatively strong anisotropy,the magnetization curves of the a and c axes were relatively close,but the magnetic moment of the b axis was much smaller.This may be due to a change in the magnetic moment component.The G-type antiferromagnetic component in the a direction in the rare earth titanate is always coupled with the A-type antiferromagnetic moment in the b direction and the ferromagnetic component in the c direction.Therefore,the antiferromagnetic to ferromagnetic change of the Ti magnetic moment in the RTiO₃ series is only the redistribution of ordered magnetic moments between three different components?G_x,A_y,and F_z?within the same magnetic symmetry.Considering that the magnetic structure of the rare earth titanate antiferromagnetic phase is the G_xA_yF_z configuration and the magnetic structure of the ferromagnetic phase is the G_xA_yF_z configuration,then due to the transitional region where we dope the sample at the phase boundary,the transitional magnetic structure may be A_y-dominant antiferromagnetic.The perpendicular and magnetic moments are more likely to deflect the magnetic moment.Therefore,the magnetic moments of the magnetization curves of the a and c axes are larger and the b-axis is smaller.The strengths of different crystalline magnetic interactions have been compared and it has been found that competition for GdFeO₃-type distortion and Jahn-Teller distortion enhances antiferromagnetic interactions in the c-axis direction,as well as orbital order and spin order separation,providing experimental basis to further understand the process of the magnetic transition of this system.