Studies of physical properties of NbTi/Co Mutilayers

• Main Authors: Wei Lurn Chang, 張維倫
• Other Authors: S.F.Lee
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/80215780457307211067

碩士 === 輔仁大學 === 物理學系 === 88 === Single NbTi films, NbTi/Co/NbTi and Co/NbTi/Co Mutilayers were grown on Si(100) substrates at room temperature by dc sputtering method. We discussed their superconductivity and ferromagnetic properties in the mixture from the resistive and magnetic measurements. The main measuring instruments we used were low temperature resistance measuring system and SQUID magnetometer. The value of superconducting transition temperature Tc decreases in general with decreasing dNbTi . Tc~9.0K as dNbTi=4000Å is close to the bulk value. when dNbTi<1000A, Tc decreases very fast. This was related to the finite-size effect of 2D thin-films. For the NbTi/Co/NbTi trilayers, we wanted to verify whether there is oscillation in Tc with increasing dCo, a signature of the π-phase states in this structure predicted in theories. Unfortunately, fluctuation in Tc due to growth condition (sputtering sequence etc.) during deposition process made it difficult for our observation. Otherwise, the dependence of Tc on dNbTi in Co20Å/NbdNbTi/Co20A、 Co100A/NbdNbTi/Co100A、Co200A/NbdNbTi/Co200A and Co500A/NbdNbTi/Co500A trilayers was similar to single NbTi films. For thinner dNbTi, the Tc shifted to lower temperature because of the stronger Cooper pair-breaking effect of Co layers, which led to the reduction of superconductivity. For the hysteresis loops in the whole series of samples which were measured below Tc, the hysteresis loops changed gradually from ferromagnetic (superconductive) ones to superconductive (ferromagnetic) ones when dNbTi(dCo) increased .we used the result to determine relative strength between ferromagnetic and superconductive effects. Otherwise,the hysteresis loops in the whole series of samples which were measured above Tc.The saturation moment per unit volume descreased when dCo decreased. Finally,we compare the results between mutilayers and trilayers data to investigate the proximity effect and if there isπ-phase existing。