| Summary: | 博士 === 國立臺灣大學 === 機械工程學研究所 === 95 === In this dissertation, we fabricate the devices incorporating cuprate/manganite heterostuctres and study their proximity effect, magnetic pinning effect and the behavior of electric-pulse-induced-resistance (EPIR) change. The process of deposition of such oxide ferromagnet/superconductor (FM/SC) multilayers using the pulsed laser deposition (PLD) technique is also demonstrated.
First of all, the current dependent proximity effects of Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers are investigated. Our experimental data show that the suppression rate of superconducting transition temperature (Tc) under the applied current (> 1 mA) is enhanced by one order of magnitude in NCMO/YBCO compared with that in pure YBCO. The enhanced Tc-suppresion is attributed to pair-breaking via the interactions with the spin-polarized quasiparticles and the magnetic exchange in association with a current-induced melting of charge-order state in NCMO.
Secondly, the magnetic pinning effect in NCMO/YBCO bilayers is investigated. It is found that by increasing the magnetic field from 0 to 5 Tesla, the critical current Ic of pure YBCO film at 50 K is suppressed by three orders of magnitude. On the other hand, in the NCMO/YBCO bilayer Ic is less sensitive to the field and maintains at the level of 100 mA at high field. This result indicates that the magnetic pining effect of NCMO is much more efficient than the conventional routes, which may be related to the fine domain structure of NCMO film.
Lastly, the electrical hysteresis in current-voltage characteristics of metal/NCMO/YBCO heterostructure, and the effect of metal/insulator interface on the resistance switching behavior are investigated at room temperature. When applying pulsed voltage of ±3 V, the Cu/NCMO/YBCO heterostructure shows resistance switching from a high- to low-resistance state with an EPIR (= (HR-LR)/LR) ratio of 25 %. On the other hand, a huge ratio as large as 1350 % is observed with ±5 V for Ag/NCMO/YBCO. Correlating the switching behavior with their current-voltage characteristics, our experimental results provide clear evidences that different metal/NCMO interfaces provide different mechanisms for the resistance switching.
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