Spin Switching Effect Of Rare Earth Orthoferrite （Er,Dy/Nd）（Fe/Mn）O₃ Single Crystals

Rare earth orthoferrites（RFe O₃,R=Y or rare earth element）,as canted antiferromagnetic materials,have many interesting and rich magnetic properties such as spin reorientation transition,magneto-optical effect,ultra-fast spin switching,and multiferroics,because of which they have aroused a significant interest in researchers from different fields.The space group of rare earth orthoferrites with distorted perovskite structures is D_2h¹⁶-Pbnm.Rare earth orthoferrites have rare earth and iron sublattices in which complex super-exchange interactions from inter-and intra-sublattices make the magnetic structure and properties of rare earth orthoferrites extremely intriguing.Among the rich properties of rare earth orthoferrites,spin switching effect and spin reorientation transition are considered to be the most likely to be applied in devices in the future,and thus have attracted much attention from researchers.In this dissertation,we have investigated the current research progress of rare earth orthoferrite and introduced the experimental methods,principles and measuring methods involved in this research.The series of single crystal samples of Er_xDy_1-xFe O₃（x=0,0.25,0.5）and Nd Mn_xFe_1-xO₃（x=0,0.1,0.2）are taken as the main research objects,and the preparation conditions for high quality single crystal growth by using the optical floating zone method were explored.The magnetic characterizations of the as-grown single crystal samples,mainly focused on spin reorientation transition and spin switching effect,were carried out.The main content of this study is as follows:1)Er_xDy_1-xFe O₃（x=0,0.25,0.5）and Nd Mn_xFe_1-xO₃（x=0,0.1,0.2）polycrystalline samples with Er and Mn ions doped into the rare earth sites of Dy Fe O₃and iron sites of Nd Fe O₃,respectively,were successfully synthesized using the solid state reaction method.The polycrystalline samples were checked by powder X-ray diffractometer,which showed that they had good phase quality with no impurities.Through the optical floating zone method,we successfully prepared their corresponding single crystal samples.Powder X-ray diffraction data of pulverized single crystals were refined in the Full Prof software to characterize their crystal structures after doping.The X-ray back-reflection Laue crystal diffraction tests showed that the single crystals have good quality.Furthermore,three crystallographic axes of the crystals were determined after multiple Laue diffraction tests in 4πsolid angle and they were cut along these directions accurately for magnetic measurements.2)The occurrence of spin switching at different temperatures in both Field-Cooling（FC）and Zero-Field-Cooling（ZFC）modes was observed in the series of Er_xDy_1-xFe O₃（x=0,0.25,0.5）single crystal samples.The abrupt magnetization drop in FC mode and jump in ZFC mode have not been reported in either Dy Fe O₃or Er Fe O₃parent single crystals.We chose the spin switching effect in Er_0.5Dy_0.5Fe O₃single crystal for a more detailed study,and found out that the triggering temperature of this spin switching effect can be tuned in an ultra-wide range from 50 to 400 K by ultra-low magnetic field.In terms of the spin reorientation transition study in this series of single crystal samples,Er_0.25Dy_0.75Fe O₃exhibits twofold spin reorientation transitions fromΓ₄toΓ₂and finally toΓ₁state upon cooling.3)We observed twofold spin reorientation transitions,i.e.,fromΓ₄toΓ₁and finally toΓ₂with cooling,in Nd Mn_0.1Fe_0.9O₃and Nd Mn_0.2Fe_0.8O₃single crystals under an external magnetic field of 50 Oe.More interestingly,Nd Mn_0.1Fe_0.9O₃and Nd Mn_0.2Fe_0.8O₃single crystals exhibit a"step-like"spin switching effect induced by magnetic field along the c-axis near room temperature.In addition,this phenomenon has an excellent repeatability,which provides the possibility for the application of this advanced material.Finally,a magnetic field induced spin reorientation transition along the c-axis is also observed,in which the closer it is to the spin reorientation transition temperature,the smaller the critical magnetic field required.