Magnetic And Transport Properties In Magnetic Topological Insulators MnBi₂Te4?Bi₂Te₃?n

The combination of magnetism and topology is a key research topic in condensed matter physics,providing a great opportunity to explore a range of emergent physical phenomena,such as the quantum anomalous hall effect(QAHE),axion electrodynamics,and Majorana fermions.However,due to the lack of suitable research materials,these strange physical effects are rarely realized experimentally.Nowadays,a series of van der Waals layered materials related to Mn Bi2Te4 have appeared,which show the interlayer ferromagnetic and interlayer anti-ferromagnetic exchange interactions.Abundant topological quantum states have been found in Mn Bi2Te4,which have outstanding characteristics.These include an anti-ferromagnetic topological insulator,a topological axion state on the surface that have long sought,a type II magnetic Weyl Semimetal with a pair of Weyl point,and a collection of intrinsic axion insulators and quantum anomalous hall insulators in even-and odd-layer films.If these properties are confirmed experimentally,they may profoundly change future research and techniques in topological quantum physics.In the forced ferromagnetic state of Mn Bi2Te4 thin layer,the observation of quantum anomalous hall conductance has attracted wide attention.However,due to the large antiferromagnetic interlayer exchange coupling,it is necessary to strengthen the external magnetic field to realize the complete polarization of magnetic moment.In this paper,the magnetic and electrical transport properties of Mn Bi4Te7 and Mn Bi6Te10 single crystals of magnetic topological insulators with van der Waals coupling are systematically studied.The single crystal sample was preliminarily analyzed and characterized by X-ray diffraction,and then the sample was packaged and prepared by a series of experimental operations,and the magnetic properties and electrical transport properties of the single crystal were measured by Physical Property Measurement System(PPMS).Then the experimental results were fully discussed,and the observed phenomena and the mechanism were analyzed.It is believed that in Mn Bi4Te7 and Mn Bi6Te10 crystals,the insertion of non-magnetic Bi2Te3 quintuple layers greatly weakens the coupling of anti-ferromagnetic exchange between layers,which leads to the decrease of anti-ferromagnetic transition temperature.The transition temperature TN of the two crystals is about 12.5 K and 11 K respectively.At low temperature,when a small magnetic field of 0.1 T-0.2 T is applied along the direction of the c axis,both of these crystals have a spin-flip transition.Due to the weak interlayer antiferromagnetic exchange coupling and magnetocrystal anisotropy,both crystals exhibit ferromagnetic hysteresis at low temperature(below 5 K),which indicates that a fully polarized ferromagnetic state can remain stable even at zero field.This is critical to the realization of the quantum anomalous hall effect.In addition,for Mn Bi4Te7 and Mn Bi6Te10 single crystals,due to their van der Waals structure,various superposition sequences of Mn Bi2Te4 septuple layer(SLs)and Bi2Te3 quintuple layer(QLs)can be realized by mechanical exfoliation.Therefore,Mn Bi2Te4(Bi2Te3)n provides an ideal platform for studying topological phases by adjusting the stacking order flexibly.