A Research On The Anomalous Hall Effect In Magnetic Topological Insulator MnBi₄Te₇ Device

Topological insulator is one of the most concerned quantum materials in condensed matter physics,which is characterized by metallic surface state protected by time reversal symmetry and insulating bulk state.Due to the non-dissipative transport property of surface state,it has a good application prospect in the fields of spintronics and quantum computing.However,it is possible to achieve novel quantum effects if the magnetic order is introduced to destroy the time-reversal symmetry in topological insulators.A classic example is the Quantum Anomalous Hall effect,the Quantum Hall effect with chiral edge states that can be realized without an external magnetic field,which was first realized by magnetic doping in topological insulators.But magnetic doping brings strong disorder and inhomogeneity of electromagnetic properties to materials,resulting that the Quantum Anomalous Hall effect was realized at extremely low temperatures.Recently,the intrinsic magnetic topological insulator MnBi2Te4 has been found experimentally,which is a typical example of the perfect combination of topology and magnetism.And it is predicted that the Quantum Anomalous Hall effect can be observed at higher temperatures than before.In MnBi2Te4,Mn ions have intra-layer FM coupling and inter-layer AFM coupling,and eventually form A-type AFM ordered structure.At the same time,the(MnBi2Te4)(Bi2Te3)n family as an intrinsic magnetic topological insulator is beginning to come into view.With the increase of n among these compounds,the distance between Mn ions of different layers increases,the AFM coupling between adjacent magnetic layers decreases,and the critical field of magnetic transition gradually decreases.Therefore,compared with MnBi2Te4,these high n members,MnBi4Te7 and MnBi6Tel0,become excellent candidates for the realization of zero-field QAHE.However,the research on MnBi4Te7 and MnBi6Te10 is not in-depth at present,especially the transport measurements of thin-layer devices are very rare,so that the research on intrinsic magnetic topological insulator is not comprehensive.In this paper,the transport properties of MnBi4Te7 thin-layer devices are studied,the unique Anomalous Hall signal is analyzed,and the inherent magnetic characteristics are discussed.In this work,we obtained nanosheets from the high quanlity MnBi4Te7 crystals,and fabricated the thin-layer devices by micro-nano fabrication technologies.The anomalous Hall effect was observed in the transport measurement,which has very unique characteristics.The most important characteristic is the anomaly hysteresis curve at-100V,that is,the Hall curve reverses in advance when the magnetic field has not crossed zero,which is different from the normal Anomalous Hall effect.Meanwhile,the Hall curve presents a hump-like nonlinear feature when approaching the saturation field.At low temperature,Fermi energy can be tunned by gate voltages,which leads to the sign reversal of the Anomalous Hall signal.The hump-like characteristics and unconventional hysteresis also change with gate voltages.Through the analysis,we put forward the explanation of superposition of two kinds of Anomalous Hall signal and made the simulation,and it is found that the coexistence of antiferromagnetic component and ferromagnetic component can explain the experimental phenomena well,in which the sign reversal is dominated by the ferromagnetic component.Furthermore,we also observed the anomalous Hall signal of temperature regulation,which fits the superposition explanation of two components and shows the modulation effect of temperature on different components.Through a series of transport measurements and simulations,the anomalous Hall signals of different components in the MnBi4Te7 device are separated,and the source of magnetism is further discussed.Our work shows that there is a more complex magnetic mechanism in MnBi4Te7.It is also helpful to the further study of the overall properties of(MnBi2Te4)(Bi2Te3),family,and provides a reference for the realization of Quantum Anomalous Hall effect in MnBi4Te7 in subsequent experiments.