龐磁阻錳氧化物表面與塊材電子結構之研究

Abstract

我們利用同步輻射高度極化的光源，進行O K edge近吸收邊緣X光吸收光譜(XANES)實驗，探討龐磁阻(CMR)錳氧化物La1-x(Ca or Sr)xMnO3 (x=0, 0.3)表面與塊材的電子結構、CMR的各異向性及對溫度的變化。全電子產率(TEY)和螢光產率(FY)XANES光譜，顯示了表面和塊材可能有不同的電子結構，原因有樣品的組成成份改變和樣品之電子結構不同。造成樣品的電子結構不同的原因，在接近基板的地方，樣品與基板之間應力較大，晶格結構被扭曲，影響了樣品的在ab平面和c軸的電子結構不同。在樣品表面因為薄膜與基板之間應力已經很弱，以及厚的樣品樣品與基板之間的應力效應相對於樣品整體的特性較弱，在ab平面和c軸的電子結構很接近，因此薄膜與基板之間應力會影響樣品表面與塊材的異同。綜合這些結果及其他實驗，可以更了解CMR錳氧化物的相分離現象及相關的研究。

The surface and bulk electronic structures of Colossal magnetoresistance (CMR) manganites La1-x(Ca or Sr)xMnO3 (x=0, 0.3) crystalline have been probed by polarization-dependent O K edge near edge x-ray absorption spectroscopy(XANES). We have also investigated the anisotropy and the temperature effects on XANES of CMR manganites. The composition and structure of samples near the surface could be changed. The latter is due to the relaxation of the strain near the thin film surface. These two factors lead to the differences between XANES of the surface and that of the bulk. Combination these results with the data from other measurements on the same sample bring the understanding on the phase separation and other related issues.