本計畫的目標是開發鐵電性與鐵磁性共存之功能型多鐵性材料，希望找到 具有龐磁電效應的新材料；並試著利用順磁離子參雜產生的磁稀釋效應或 化學壓力來改變系統自旋的受挫程度，或利用基板的應力效應與退火條件 來調整薄膜樣品的電極化強度，以提昇現存的多鐵性材料之磁電耦合強 度。我們亦將使用脈衝雷射蒸鍍法製作以多鐵性材料(反鐵磁)為絕緣層，巨 磁阻(鐵磁)為電極的磁穿隧結。藉由電場(電壓)極性的改變來調整多鐵性材 料層的磁化方向，利用存在於鐵磁-反鐵介面間的交換偏置場來改變巨磁阻 層的自旋組態，探討電壓調控磁穿隧結之磁組態的可行性。實驗上，我們 將在外加磁場的環境下測量樣品的電極化強度、介電常數、磁性、比熱、 拉曼光譜，有系統地研究多鐵性材料複雜的磁電性質與晶體對稱性、磁結 構之間的關聯性，預期對多鐵性材料自旋、電荷、晶格自由度間的耦合機 制有更完整的理解，這對設計更有智慧的磁電材料並調控其功能性以符合 磁紀錄鐵電儲存元件的需求是極為重要的。 We propose to search for new classes of multiferroics which have colossal magnetoelectric effects and to optimalize coupling between magnetization and electrical polarization of existing systems by means of paramagnetic doping induced magnetic dilution, modification of spin frustration with chemical pressure and strain. In addition, we plan to fabricate FM/AFM/FM magnetic tunnel junctions by pulse laser deposition technique where ferromagnetic metal colossal magnetoresistive materials and antiferromagnetic multiferroics will serve as electrodes and an insulating barrier, respectively. We propose to study electric field-induced magnetization switching in ferromagnetic electrodes through exchange bias coupling. By extensive studies on structural, electrical, optical, and magnetodielectric properties of materials investigated, we have a great opportunity to gain new understanding about underlying mechanism of the novel magnetoelectric effect as well as the interplay among spin, charge, and lattice degrees of freedom of multiferroic materials. The understanding physics of multiferroics will provide key information about designing smarter multiferroic materials and control their functionality for practical applications such as magnetically recorded ferroelectric memory.
