| The exploration of topological materials is currently one of the important topics in the condensed matter physics,because they exhibit many exotic physical phenomena.The discovery of topological materials from two-dimensional quantum well systems and three-dimensional topological insulators,to topological semi-metals,topological superconductors,etc.,has provided a research platform for novel physical phenomena such as quantum Hall effect,topological magnetoelectric effect,Majorana fermions,etc.More importantly,when magnetism meets topology,many important and novel physical phenomena are born,which further stimulate researchers’interest.This dissertation mainly focuses on the anomalous physical properties of the intrinsic antiferromagnetic topological insulator material MnBi2Te4system,and explores the correlation between its magnetism and topology.In the paper,we have grown the high-quality MnBi2Te4single crystals through the method of self-melting flux,and the single crystal was analyzed by scanning electron microscope and X-ray diffractometer for its composition and structural characterization.Then,MPMS and PPMS were used to perform systematic magnetic electrical and thermal transport properties measurement.We found that:（1）A large MnBi2Te4single crystal was successfully grown,and its lattice structure and related parameters were determined;the magnetic measurement data confirmed that the antiferromagnetic transition Curie temperature（TN）of 25 K,and c-axis is its easy magnetization axis.A large magnetic anisotropy is observed at low temperature.When the external magnetic field gradually increases,the system undergoes a continuous phase transition from antiferromagnetic ferromagnetic-to-ferromagnetic.（2）The resistance measurement shows that the sample sharply drops near 25 K due to the spin scattering effect,which is consistent with the behavior of antiferromagnetic transition;when an external magnetic field is applied,the system exhibits a large negative magnetoresistance.The measurement of Hall resistance vs magnetic field shows that the system exhibits abnormal Hall effect at low temperature;when 3 T<B<6 T,the Hall resistance obviously deviates from the linear behavior and increases sharply;（3）The thermopower of the system drops sharply at the antiferromagnetic transition temperature,and the external magnetic field can induce a large magneto-thermoelectric coefficient.The Nernst increases with the increase of temperature,which is different from the characteristics of traditional metals,which may come from the stronger spin fluctuations in this system. |
