磁性層覆蓋之電荷有序錳氧化合物之磁電傳輸特性研究

Abstract

在La1-xCaxMnO3相圖中，x = 0.5時，La0.5Ca0.5MnO3塊材的特性會從順磁-絕緣態轉變成反鐵磁-電荷有序-絕緣態，電荷有序轉變溫度TCO = 220 K。本實驗利用基板對La0.5Ca0.5MnO3薄膜應力(strain)的影響，成功製備出La0.5Ca0.5MnO3(200)薄膜，其電阻對溫度的變化顯現出明顯的熱滯(hysteresis)現象，應為薄膜擁有電荷/軌道有序的現象。我們選用兩種基板分別為SrTiO3(110)與LaAlO3(110)，使LCMO薄膜在bc面上的MnO6八面體受應力影響，電流方向沿著b軸與c軸方向，R-T表現之特性與相變溫度不同。隨著時間演進，La0.5Ca0.5MnO3(200)薄膜的電阻熱滯現象消失；覆蓋鐵層後，Fe2O3/La0.5Ca0.5MnO3(200)薄膜的電阻熱滯現象被保存下來。

We successfully obtained the charge/orbital ordering properties by epitaxial the La0.5Ca0.5MnO3 thin films on SrTiO3(110) and LaAlO3(110) substrates. However, the observed charge/orbital ordering temperature (TCOO = 120-140 K) is substantially lower than that reported for bulk (TCOO = 220 K), presumably due to the epitaxial strain existing in these films. Furthermore, unlike the bulk material where the TCOO has been found to coincide with the paramagnetic-antiferromagnetic transition temperature (Neél temperature), we found that the Neél temperature of the LCMO(200)/LAO(110) and LCMO(200)/STO(110) thin films occurs at much lower temperatures (=60-90 K) with an apparent anisotropy. Coating a Fe2O3 layer on top of these films appeared to provide protection to the surface of LCMO thin films from air and the resistance hysteresis behavior of charge ordering could be retained even after cyclic measurements.