La1-xMnO3薄膜的物理特性及x光吸收光譜研究

Abstract

和La1-xCaxMnO3一樣具有金屬-絕緣相變的La1-xMnO3薄膜已被我們所研究。為了比較，La0.67Ca0.33MnO3和La0.67Sr0.33MnO3薄膜也一同被研究，其中包括傳輸及磁性的性質。在我們的實驗中，除了LaMnO3外，其他樣品皆具有幾乎同時發生的金屬-絕緣相變及鐵磁轉變。 在電子結構方面，我們使用x光吸收光譜來加以探討。令人驚訝的是：La1-xMnO3 La0.67Ca0.33MnO3及La0.67Sr0.33MnO3在x光螢光吸收光譜顯示其電子結構具備有極大的異向性，但是在全電子產率卻是同向性。此行為告訴我們這些混合物所製成的薄膜在表面及裡層結構有極大的不同，我們試著以晶格扭曲的觀點來解釋這些成分的異向性。

We have studied La1-xMnO3 thin films, which show the metal-insulator transition similar to the divalent-doped system such as La1-xCaxMnO3. In order to compare, we also studied La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3. The transport and magnetic properties were measured. In our experience, all the samples, except LaMnO3, show the coexistence of the metal-insulator transition and ferromagnetic transition. X-ray absorption spectroscopy was employed to investigate the electronic structure. Surprisingly, the electronic structure of La1-xMnO3, La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 shows large anisotropy in fluorescence yield mode although it is isotropy in total electron yield mode. This behavior tell us the thin films of La1-xMnO3 system, La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3, are different between surface and bulk. From the change of O K edge XANES around Mn 3d associated peak, Mn 3d associated peak seem not to be responsible for the metal-insulator transition and the associated magnetic ordering. We also report the anisotropy of the O K edge spectra of La1-xMnO3 and the depression of the Mn 3d associated peak due to La deficiency. These results are explained in the context of a decrease in the Mn-O-Mn bond angle along the a, b axis.