Investigation Of Magnetism And Electrical Transport On Magnetic Semimetal DySb And Eu₂Ir₂O₇ Single Crystals

Topological semimetal is one of most important breakthroughs in condensed matter physics in recent decades.Among the topological candidate materials,magnetic topological semimetal can exhibit various interesting quantum phases and unusual exotic physical properties due to the coexistence and interplay between nontrival electronic structure,magnetic structure,obital order and strong electron correlation effect.In this thesis,we investigate the magnetic and electrical transport of antiferromagnetic（AFM）semimetal for Face-centered-cubic（FCC）DySb and Pyrochlore Eu₂Ir₂O₇ single crystals,as typical examples of AFM semimetal with non-collinear spin structure.To establish the interplay between magnetic structure and charge electrons of DySb and Eu₂Ir₂O₇ antiferromagnetic semimetals,the main contents of our research are summarized as follows.In 1^st part,we present a breif introduction on the concept,related materials,exotic quantum phenomenons and physical pictures of magnetic topological semimetals in past decades.Then,we emphasize on the discussion of novel physical properties in the antiferromagnetic semimetals with non-collinear magnetic structure,such as chiral negative magnetoresistance,topological anomalous hall effect and large intrinsic anomalous hall effect.Based on the analysis of the recently discovered topological phenomena and related physical behaviors in RX（R=rare earth,X=Sb,Bi）magnetic semimetal and pyrochlore R₂Ir₂O₇ iridite（R=Y,Rare Earth）,we propose our research’s motivation in this thesis.In 2^nd part,we present the crystal growth,microstructure analysis and physical characterization of DySb and Eu₂Ir₂O₇ single crystal,including the related principle on physical measurement.In 3^rd part,we explore the the interplay between magnetic structure and electronic transport on DySb,as an Ising-type antiferromagnetic（AFM）semimetal.Below T_N¹0.2 K,magnetic measurements reveal that DySb shows a metamagnetic transition from AFM phase to intermediate HoP-type phase and full polarized ferromagnetic（FM）state for magentic field（B）along easy[001]axis.Field dependence of longitudinal and transverse hall resistance show strong anomalies near the metamagnetic transitions from AFM phase to intermediate HoP-type phase and full polarized ferromagnetic（FM）state.At 2 K,angle dependent MR displays a four-fold symmetry behavior as field（B）rotating within（110）or（100）plane,where the maximum magnetoresistance can change to[111]axis from[110]axis under magnetic field.For B//[001]axis,field dependent anomalous hall resistivity displays opposite sign response to B for the 1^st and 2^nd metamagnetic transitions arising from the rearrangement of magnetic structures with different spin chirality.Moreover,giant anomalous hall conductivity（AHC）reaches⁵000?^-1?cm^-1 owing to the combined effect of compensated semimetal and noncoplanar magnetic textures.In 4^th part,we firstly study the chemical stoichiometric effect on metal-insulator transition in Eu_2（1+x）Ir_2（1-x）O_7-y with different Eu/Ir ratio.The transition temperature(T_MI)is decreased from 116 K（Eu/Ir=1.015）to 102 K（Eu/Ir=1.05）.The main work is to confirm the existence of interfacial exchange coupling between“All-in-all-out”（AIAO）antiferromagnetic（AFM）domain and its’domain wall based on magnetism and electrical transport results for Eu_2（1+x）Ir_2（1-x）O_7-y single crystal.After field cooling procedure from T>T_N,the isothermal magnetization（M-H）curves show asymmetric behavior,namely the existence of exchange bias effect in contrast to the zero-field symmetric M-H curves.And the more stoichiometric samples show more distinct asymmetic behavior,indicates the existence of exchange coupling of AIAO AFM domain and its’domain wall with net ferromagnetic（FM）moments.Interestingly,further electrical transport studies show that the interfacial coupling of AIAO domain/domian wall can induce asymmetric longitudinal magnetoresistance and transverse Hall effect,the temperature dependence on this asymmetric electrical transport is also discussed.