The Research Of Coexistence Of Ferromagnetism And Superconductivity In Cr-doped FeTe_0.8S_0.2and Multiple Superconducting Phase In Pressured NiTe_2-?

Since discovered from graphite in 2004,graphene sets off a wave of research due to its bizarre physical properties.With the advent of graphene,two dimensional materials have attracted more and more attention in the field of condensed matter research,such as Fe Te S superconductors and transition metal dichalcogenides,which have maintained considerable heat.In this paper,we have studied the superconductivity and magnetic properties of Cr-doped Fe Te_0.8S_0.2,which fills the gaps in related research fields.For transition metal dichalcogenides,we found multiple superconducting phases in the pressured Ni Te_2-?single crystal.Our experimental results are as follows:?1?We doped the Cr element on the Fe site of Fe Te_0.8S_0.2,synthesized polycrystalline samples with doping concentrations of 0%,2%,4%,and 6%,respectively,and conducted superconducting and magnetic measurement.We found that in the doped Fe_1-xCr_xTe_0.8S_0.2 system,the coexistence of super-conducting and ferromagnetic phases occurs.XRD experiment shows that Cr element is more inclined to enter the interlayer of the two-dimensional material Fe Te_0.8S_0.2,so that the c-axis is significantly increased.On the one hand,the effect of doping on the superconducting state is weakened.On the other hand,the Cr element between the layers forms ferromagnetic order at low temperature,leading to the appearance of ferromagnetism.Electrical transport and magnetic experiments confirmed the coexistence of ferromagnetism and superconductivity in the Cr-doped Fe Te_0.8S_0.2 system,which provided more experimental guidance for the study of multiphase coexistence.?2?We obtained the Ni Te_2-?single crystal sample by self-flux method,and studied its electrical transmission behavior under pressure.In the pressure range of0-51.0 GPa,Ni Te_2-?single crystal has undergone two different superconducting phases SCI and SCII.The zero resistance temperature of SCI is 2-4K,while that of SCII is around 7K.The superconducting phase SCI begins to appear at 0.5 GPa in sample,and the superconducting transition temperature reaches its maximum at 4.2GPa with T_c^zero?4.2K.Between 4.3-33.1 GPa,SCI is suppressed by pressure,and T_c^zero keeps dropping to 2.2K.Between 33.1-47.2 GPa,the sample begins to appear SCII superconducting state,and the two superconducting phases coexist.In this pressure region,SCI is continuously weakening,while SCII is continuously increasing.At higher pressures,SCII shows complete zero resistance,dominating the RT diagram.High-pressure Raman indicates that the sample has undergone a structural phase change at around 35 GPa,which is responsible for the newly emerged superconducting phase SCII.