臺灣博碩士論文加值系統

本篇研究的主要目的乃利用固態反應法 (Solid State Reaction)
合成一系列錳系具巨大磁阻效應之新材料；此種磁感測元件具應用
之潛力，未來被預測可用於磁頭器件。本研究主要合成具
[RE,(Sr,Ca)]n+1MnnO3n+1，其中n = ∞的化合物有三種：
為 a: Nd1-xCaxMnO3 ( x = 0 ~ 0.5 )，b: Nd1-xSrxMnO3( x = 0 ~ 0.5 )
，c: Nd0.7(Sr0.3-yCay)MnO3 ( y = 0 ~ 0.3 ) 均為長方晶系 ( orthorhombic )
之Mn-O八面體的三維結構。而n = 2的化合物有 d: Ln1+xSr2-xMn2O7，
Ln = La、Pr和Nd ( x = 0，0.2和0.4 ) 的四方晶系 ( tetragonal )
之Mn-O八面體的二維結構。本研究所涵蓋的材料特性分析技術為：
( 1 ) 以X光粉末繞射之結構精算，得知因摻雜所造成的晶格變化，
( 2 ) 以同步輻射X光吸收近吸收邊緣結構光譜 ( X-ray Absorption Near Edge
Structure Spectrum；XANES ) 之方法得知樣品之錳的混合價數，
( 3 ) 藉由超導量子干涉儀量測樣品之磁性變化，
( 4 ) 以量測電阻和磁場之間的交互作用得知樣品之磁阻值。
藉由上述之分析技巧，得以研究稀土族元素與鹼土族元素之摻雜，
及二維結構與三維結構之不同，其對巨大磁阻效應所產生的影響，
進而促進對導電機制之瞭解，使此材料得以更接近實用化。

New bulk polycrystalline ferromagnets [ RE,(Sr,Ca) ]n+1MnnO3n+1
( n = 2 and ∞ ) with colossal magnetoresistance ( CMR ) have been
successfully synthesized. Such phenomenon can be useful for various
magnetic and electric device applications in the near future.
The n = ∞ system containing (a) Nd1-xCaxMnO3 ( x = 0 ~ 0.5 ),
(b) Nd1-xSrxMnO3 ( x = 0 ~ 0.5 ) and (c) Nd0.7(Sr0.3-yCay)MnO3
( y = 0 ~ 0.3), all the compounds exhibit a orthorhombic crystal
structure and three-dimensional electrical and magnetic behavior.
The n = 2 system containing Ln1+xSr2-xMn2O7 (Ln = La, Pr and La;
x = 0 ~ 0.4 ), all the compounds have a tetragonal crystal structure
and two-dimensional electrical and magnetic behavior.
In this research, we use the following technologies for the studies :
(1) powder X-ray refinement to understand the crystal structure,
(2) X-ray Absorption Near Edge Structure Spectrum (XANES) to measure the
valence of manganese ion, (3) superconducting quantum interference design
(SQUID) magnetometer to determine the magnetic properties, (4) electrical
resistivity to measure the magnetoresistance value. Based on the analysis
results, we can understand the detailed mechanism of the colossal
magnetoresistance effected by the chemical substitution on the titled
systems.