Electrical And Magnetic Properties Of RSi(R=Co,Fe)single Crystal At Low Temperature

Weyl semimetal is an important material for researching Weyl fermions,and it has unusual behaviors in magnetic and electrical properties.Transition-metal monosilicides(CoSi,FeSi,Rh Si,Mn Si,etc.)-a class of Weyl semimetals,are being recognized more clearly with the advancement of technology.The band structure of CoSi observed by ARPES proves that it has many kinds of Weyl fermions,which leading to a new research fever to academia.The Weyl fermions phonon energy spectrum of FeSi and its three-dimensional topological insulator properties have attracted people's attention.We used Ga and Te as flux to grow CoSi single crystal samples,and Ga flux to grow FeSi single crystal samples.Using X-ray diffraction,scanning electron microscope observation and energy spectrum analysis to characterize the single crystal samples,showed that the high quality of CoSi and FeSi,which demand for magnetization and electric transport measurements.We used the magnetic property measurement system(MPMS)to characterize the magnetic properties of CoSi single crystals and FeSi single crystals.The results showed that CoSi single crystals grown with different fluxes behaved differently under an applied magnetic field.The CoSi single crystal grown with Ga flux exhibits paramagnetism at 6-300 K,while the sharp decrease in magnetic properties at 6 K is due to the Ga residue in the single crystal.The CoSi single crystal grown with Te flux shows diamagnetism at 2-300 K,and there occur a local magnetic moment at low temperature.The FeSi single crystal exhibits a transition from antiferromagnetic to paramagnetic with decrease of temperature.We also used a physical property measurement system(PPMS)with strong magnetic field and low-temperature to characterize the electrical properties of CoSi single crystals and FeSi single crystals.The resistance of CoSi single crystal grown by Ga flux suddenly drops at 6 K,which is consistent with the phenomenon of magnetic measurement,we attribute it to the superconductivity of Ga.In contrast,there is no significant electrical change at low temperature for the CoSi single crystal grown by Te flux.CoSi single crystals grown with two different fluxes both exhibit negative magnetoresistance,indicating it is an intrinsic characteristic of CoSi.Due to the weak magnetic appears at low temperature,the time inversion symmetry of the system is destructed,leading to the disappearance of weak anti-localization(WAL).Therefore,CoSi exhibits positive magnetoresistance.The reason of negative magnetoresistance above 30 K is attributed to the weak anti-localization of many fermions in CoSi under the magnetic field.The RT curve of FeSi single crystal shows a decrease in resistance below 29 K,indicating the transport is gradually dominated by surface state.The relationship between the surface state of FeSi single crystal and its anisotropic magnetoresistance at low temperature needs further study.These results enrich the study of CoSi and FeSi single crystals,and help to further understand the physical connotation of various fermions in single silicon compounds.