以雷射脈衝沉積法成長CaMn7O12薄膜之結構與磁特性分析

Abstract

近年來，斜方六面體(Rhombohedral)結構的CaMn7O12被發表為一種新的磁電耦合多鐵材料。此材料在沿c軸方向上，具有巨大的非正規鐵電極化率(~2870 C/m^2)，且與在尼爾溫度90K時發生的反鐵磁相轉變有強烈的耦合關係。與同類材料相比，同時擁有至今最高的鐵電極化率及有序相轉變溫度。然而近年來相關的研究及量測大多以單晶為主，缺少成長CaMn7O12薄膜相關的研究。考慮到CaMn7O12的各向異性(anisotropy)，成長CaMn7O12為軸向明確的薄膜，將會是一個深具潛力的方向，不僅有助於發展至應用面，並可望獲得更高的鐵電極化率。 在本研究中，即嘗試成長CaMn7O12薄膜於不同基板上。實驗先分別利用凝膠法和高純度單晶製作CaMn7O12靶材，再以脈衝雷射沉積法(PLD)將CaMn7O12薄膜分別成長於SiO2、MgO和SrTiO3基板上，再以X光繞射儀和超導量子干涉儀量測薄膜的結構與磁特性，一一分析比較，了解不同基板及成長條件與CaMn7O12薄膜特性的關係。

Recently, rhombohedral phase CaMn7O12 has been reported as a new magnetic multiferroic material exhibiting an unprecedented giant improper ferroelectric polarization (~2870 C/m^2) along c-axis strongly coupled to the antiferromagnetic magnetic transition at the Néel temperature of 90 K. However, the investigation of this material in thin film form is largely lacking, which inevitably is very important for application and in order to harvest the giant magnetically induced polarization anticipated. In this study we have tried to grow the CaMn7O12 thin films on different substrates. The targets were prepared by pressing the CaMn7O12 powder derived from sol-gel method and high quality single crystals obtained by flux melting growth method into 1-inch pellets. We grew CaMn7O12 thin films on the the SiO2 substrates, the MgO substrate, and the SrTiO3 substrate respectively by pulsed laser deposition. Then we measured and analysed the structure and magnetic properties of the thin films on different substrates. The results of X-ray diffraction pattern and magnetic susceptibility measurements will be presented and discussed.