Electrical Transport And Magnetic Properties In Ln₃TiSb₅?Ln=La?Ce? System

Since superconductivity was discovered by Onnes in 1911,over a century has witnessed its development and history.Superconducting materials show some exotic transport properties and rich electronic state phase diagram when magnetism is introduced.Thus,exploring new superconducting materials and studying its properties have become very hot and key issue in condense matter fields so far.Ternary rare-earth transition metal antimony Re_xM_ySb_Z compounds have been investigated for over three decades,but the previous researches focused on looking for the unknown compounds and their magnetic properties.Superconductivity and the effect of magnetism elements in those systems are less known.In this dissertation,we mainly investigate the electronic and magnetic behaviors of the Re₃TiSb₅?Re=La,Ce,Pr?compounds through transport measurements,in particular for the superconductivity and magnetism of 4f-electrons in Re₃TiSb₅?Re=La,Ce?.On the other hand,the origin of superconductivity and magnetic phase transition are investigated and discussed.The framework of this dissertation consists of four chapters:Chapter one,we introduce the history and development of superconducting materials;Chapter two is about the basic methods for growing single crystals in Ln₃TiSb₅?Ln=La?Ce?,measurements and some experimental equipment we used.Chapter three,we discuss the superconductivity and magnetism of Ln₃TiSb₅?Ln=La?Ce?by performing the measurements of EDX,magneto resistivity,magnetic susceptibility and specific heat.Our results are summarized as listed:The large single crystals of La₃TiSb₅ and Ce₃TiSb₅ are grown by Sn-flux methods.The EDX analysis confirms the chemical compositions,almost closed to the stoichiometric ratio3:1:5.But some samples also show that very tiny impurities Sn are detected by the measurement of EDX.In La₃TiSb₅,we perform those measurements on three samples.As a result,we find that resistivity of sample 2 drop rapidly while other samples are not observed down to 2 K.The diamagnetic signal for three samples can be observed but the superconducting magnetic shielding volume fraction estimated by ZFC data is less 10%at 2 K.Meanwhile,no any abnormal around 4 K can be observed in heat specific data.We thus believe that La₃TiSb₅ does not display superconductivity above 2 K,different to the previous reported.The drop resistivity and diamagnetic signal about 4 K may be from the impurities phases Sn.In Ce₃TiSb₅ system,the rich magnetic phase transitions were observed through measuring its resistivity,magnetization,and heat specific.At low magnetic fields less 1 T,the sample shows the antimagnetic behavior at 5 K,while it displays the ferromagnetic behavior when magnetic field is over 1 T,implying a Cant-magnetic structure in the present sample.The negative magnetoresistivity is observed at low temperature,and it decreases rapidly to several percentages with temperature warming up to50 K.The heat specific shows an abrupt jump at around 5 K,indicative of the magnetic phase transition.This jump becomes broad and shifts to low temperature below 1 T,while goes to the high temperatures as B is over 1 T.We thus suggest that the sample undergoes a ferromagnetic transition under magnetic fields.The last part of the article we summarized and reflected on the research process of this article,and proposeed several possibilities for our study of La₃TiSb₅ and Ce₃TiSb₅ in the future.