複雜自適應物質之研究---子計畫五---龐磁阻與多鐵性錳氧化物之相分離與尺寸效應研究

Abstract

90 年代初期，鈣鈦礦結構金屬氧化物中觀察到龐磁阻、相分離與豐富的相圖等現象 引起廣泛的注意。到了1999 年多鐵性材料因磁電效應及其未明的機制再度引起學者的 注目。在強關連電子系統中，自旋、電荷、電子軌域與晶格間的作用對電子傳輸機制扮 演著重要的角色。本計畫將與其他子計畫配合，製備各種龐磁阻材料與多鐵性材料的薄 膜，並藉由各種分析工具在不同溫度、磁場、電場下，觀察這些外在因素對相分離及相 關的物理特性的影響，以釐清當中的機制。未來三年的研究計劃中，除了將以電子穿隧 顯微鏡，配合本實驗是近年來發展的穿隧能譜成像技術，研究次微米尺度的的相分離現 象和相的分佈之外，亦將結合電子束微影和離子蝕刻等技術，並配合其他子計畫，製作 微小結構以及次微米尺度的量測與分析，以探索尺寸效應對衍生相分離現象的主要作用 的影響。本計劃將過去所建立的儀器技術與知識背景在三年中擴充並加以應用在多鐵性 材料上，以求對強關連電子系統金屬氧化物薄膜的物理特性做更深入的研究。

In recent decade, colossal magnetoresistance, phase separation, and the associated rich phase diagrams have been extensively explored in various strongly correlated systems, particularly in perovskite manganites. However, there are still many unresolved mysteries, as what is the role played by the phenomena of phase separation on the associated magneto-transport properties and phase transitions. Furthermore, since 1999, the re-discovery of multiferroics has revived the attention of the intriguing magnetoelectric effect existent in materials generally classified as the complex adaptive matters. In strongly correlated electron system, transition metal compounds show the complex interplay among the spin, orbital, charge, and lattice degree of freedoms. Yet none of them was dominant enough to determine the physical properties of the system. As a result of the competition, the system tends to compromise and allow the coexistence of several robust phases even in conditions well into the global phase transition revealed by magnetization or transport measurements. In this proposal, we plan to look into the fundamental physics behind these emergent phenomena. We will incorperate with related proposals to grow perovskite manganites and multiferroics thin films by pulsed-laser deposition. Then by performing extensive experiments on transport properties, magnetic transitions, electric ordering, x-ray absorption spectroscopy, scanning tunneling microscopy, it is anticipated that the current understanding of these systems can be further advanced. Also as being inspired by our previous studies on the colossal magnetoresistive systems that the separated phases are all in a length scale of about submicron range, it is very interesting to combine the techniques of the electron beam lithography and ion milling to create structures with comparable sizes to explore the effects of size constraint on the phase separation phenomena. These concept will also be extended to study the even more interesting multiferroic counterparts.