The Single Crystal Growth Zr_1-xNb_xCo₂Sn And The Physical Properties Study Of Topological Semimetals

This thesis is mainly concerned with the synthesis,magnetism and transport properties of a magnetic Weyl semimetal candidate:Zr_1-x-x Nb_xCo₂Sn,as well as single crystals growth and transport properties study of some topological materials.The main content was summarized as follows:1.A series of single crystals Zr_1-xNb_xCo₂Sn were synthesized via Sn-flux.The EDX shows the composition of the single crystals and the amount of every element,so we can obtain the value of x.The position and occupation of all atoms were summarized from the single crystal X-ray diffraction?XRD?.The Nb atoms replace about 30 percent of Zr atoms which is almost consisting with the nominal doping concentration x=0.275.What's more,the position and occupation of the other atoms has not been changed.The powder XRD patterns presented that the crystalline structure was not changed with the doping of Nb and the space group was still Fm-3m?#225?.The lattice parameters can be obtained by indexing process of the powder XRD data.With x increasing,the lattice parameter decreases.The single crystals are soft magnetic materials with H_C³00 Oe and the moment quickly saturated at low fields.As x increasing,the Curie temperature shifts to low temperature,the ferromagnetism becomes weaker and the saturated moment diminishes.In addition,the resistivity increases and the broad peak moves to low temperature,consisting with T_C.The metallic behavior changed to insulating behavior with increasing x.The magnetoresistance is positive below 50 K.The negative MR is observed above 50K and the maximum value of it is around T_C.For x=0.275,the kink at low field is caused by the ferromagnetic order.With the temperature rising,the kink shifts to high field.The angle dependent MR shows a very weak correlation with angle.Moreover, Zr_1-xNb_xCo₂Sn showed a very large anomalous Hall Effect,which is caused by magnetism.With x increasing,the Hall resistivity increases.2.A series of single crystals for topological materials have been successfully synthesized via flux method,such as La Bi?Na₃Bi?CuMnAs?LaSbTe?CaAgP?CaAgAs?WTe₂?Cu₂S?Bi₂TeI,and so on.We use the chemical vapor transitionmethod to grow the magnetic Weyl semimetal HgCr₂Se₄ and Dirac node-line semimetal ZrSiS.The low temperature magnetoresistance?MR?of Ti B₂ single crystals was measured in PPMS.Unsaturated MR was observed when the applied field was perpendicular to the electric current at 2 K,but the oscillation was not observed until increasing applied field to 14 T.When the applied field was parallel to the electric current,a smaller MR was observed.The MR was dependent to the angle between applied field and current orientations.