Single Crystal Growth And Electrical,Magnetic Properties Of Antiferromagnetic Topological Semimetal AMnSb₂（A=Eu,La）

In recent years,topological materials have been one of the research hotspots in condensed matter physics.Topological materials are mainly divided into topological insulators,topological semi-metals and topological superconductors,etc.Topological semimetals are another important topological material after topological insulators.There are many unique physical properties in topological semimetals,such as:anomalous Hall/Nernst effects,chiral anomaly magnetoresistance,and extremely large magnetoresistance effect,etc.In layered manganese pnictides AMn Pn₂（A=Ca,Sr,Ba,Yb;Pn=Sb or Bi）,Theoretical studies predict that checkerboard-like square net（or distorted zigzag chains）formed by Bi or Sb could host Dirac states.Therefore,this system can serve as an important platform for exploring new topological materials and investigating the coupling between magnetism and topological bands.In this paper,we report the single crystal growth of Eu MnSb₂ and La Mn_1-xSb₂,and systematically studying their structure,magnetic properties,and transport properties.The main results are shown as follows:1.We successfully grew out high-quality metal EuMnSb₂ single crystals using the flux method.Large Hall signals up to room temperature were observed,indicating that transport properties is dominated by the hole carrier with high mobility.There are two sets of magnetic lattices for Eu and Mn in Eu MnSb₂,respectively.The coupling between Eu and Mn sublattices leads to the complex magnetic ground states in Eu MnSb₂.We establish magnetic phase diagram for two crystallographic directions through the magnetic and transport measurements.According to the phase diagram,two consecutive magnetic transitions can be attributed to antiferromagnetic transition（24 K）and spin orientation（9 K）of Eu sublattice,respectively.We observed quantum oscillations below 30 K.We obtained the information for the band characteristics of the Eu MnSb₂ through the analysis of quantum oscillation signals,such as the oscillation frequency,effective mass,and Berry phase.We observed that magnetoresistance（MR）,quantum oscillation,and Berry phase are significantly affected by antiferromagnetic transitions,and strong coupling between charge transport,energy bands,and magnetic order can be concluded.This research work provides an important platform for investigating the coupling between magnetism and topological bands.2.We used the flux method to grow high-quality LaMn_1-xSb₂single crystals,and performed systematic measurements of the magnetic and transport propertiesof La Mn_1-xSb₂.he crystal structure and chemical composition of La Mn_1-xSb₂ were determined by X-ray powder diffraction refinements,transmission electron microscopy（TEM）,and EDS measurements.Mn vacancy were induced by the charge balance effect,which has a profound influence on the magnetic and hence transport properties.Magnetization measurements reveal an antiferromagnetic transition at T_N=130 K.At low temperatures we observed non-monotonic negative magnetoresistance behavior.The transitions in magnetoresistance agree well with those in the magnetization measurements,indicating their magnetic origin.The above results show thatvacancy could tune the magnetism of antiferromagnetic topological semimetal,and then the topological properties.