臺灣博碩士論文加值系統

我們架設了測量熱電動勢 ( thermoelectric power ) 的實驗裝置,並運用此儀器去
測量具有超大磁阻的錳氧化物的熱電動勢。在實驗方面,熱電動勢的原理,實驗上的配備,
以及一些實驗上的細節將會在本論文中做一一介紹。在超大磁阻材料方面,我將一一介紹
double exchange , Jahn-Teller effect 等觀念,以及charge ordering 的現象。在實驗
結果的討論上, 將會探討熱電動勢如何反應出局域化和非局域化的行為,我們的結果顯示
除了局域化的效應之外,自旋散射也是導致絕緣體-導體轉換的機制。我們也觀察到某些系
列的樣品中具有特殊的熱遲滯現象 ( thermal hysteresis ),我們將會對這些現象作一些
分類和討論。另外, 對於在相圖中所呈現的對稱與非對稱性的問題 也將作一些釐清。

We have set up the experimental facility for measuring the thermoelectric
power (TEP) of some colossal magnetoresistance (CMR) materials. The concept o
f TEP, the details of the experimental setup, and the consideration of experim
ental techniques will be discussed in order. For tthe aspects of CMR materials
, the concept of the double exchange model, the Jahn-Teller effect, and the ch
arge ordering phenomenon will be briefly introduced. For the experimental resu
lts, we will show how the behavior of TEP reflects the localization and deloca
lization effects. Our result suggests that, except the localization effect, th
e impurity or spin scattering can be another mechanism responsible for the ins
ulator-metal transition. We also observe thermal hysteresis exhibited in some
samples. We will classify them and discuss their distinct features. The final
part of the thesis will focus on the symmetric and asymmetric behavior exhib
ited in the phase diagram.