Extremely Fast Optical and Nonvolatile Control of Mixed-phase Multiferroic BiFeO3 via Instantaneous Strain Perturbation
光誘發之應力脈衝對多鐵性材料引致之超快速非揮發性操控
Y.-D. Liou, S.-Z. Ho, W.-Y. Tzeng, Y.-C. Liu, P.-C. Wu, J. Zheng, R. Huang, C.-G. Duan, C.-Y. Kuo, C.-W. Luo, Y.-C. Chen, and J.-C. Yang*
2021/06/01
Multiferroics—materials that exhibit coupled ferroic orders—are considered to be one of the most promising candidate material systems for next‐generation spintronics, memory, low‐power nanoelectronics and so on. To advance potential applications, approaches that lead to persistent and extremely fast functional property changes are in demand. Herein, it is revealed that the phase transition and the correlated ferroic orders in multiferroic BiFeO3 (BFO) can be modulated via illumination of single short/ultrashort light pulses. Heat transport simulations and ultrafast optical pump‐probe spectroscopy reveal that the transient strain induced by light pulses plays a key role in determining the persistent final states. Having identified the diffusionless phase transformation features via scanning transmission electron microscopy, sequential laser pulse illumination is further demonstrated to perform large‐area phase and domain manipulation in a deterministic way. The work contributes to all‐optical and rapid nonvolatile control of multiferroicity, offering different routes while designing novel optoelectronics.
對於高速、高儲存密度且節能的非揮發儲存元件的持續開發與探索是發展雲端運算與大數據分析等資訊科技的關鍵。鐵酸鉍(BiFeO3 , BFO)的室溫鐵有序參量包含了鐵電、反鐵磁以及弱的鐵磁矩相互共存且耦合，以此為基礎有望能展示出多位元記憶體的功能特性。然而，受限於鐵疇域壁移動速度，現行之電場為主的操控難以突破奈秒時間尺度。在此研究中，我們對BFO進行適當的磊晶應力調製，形成類長方晶相(T-like)與類菱長方晶相(R-like)共存的”混相”結構，並藉由奈秒到飛秒時間尺度的單發聚焦雷射脈衝照射，成功地實現高速且非揮發之晶相與鐵有序操控。我們發現極短的雷射脈衝能直接驅動混相BFO到T-like相BFO的轉變。藉由國家同步輻射TLS13A,17B與09A的高解析X光繞射(high-resolution x-ray diffraction)以及TPS45A的次微米軟X光能譜(submicron soft x-ray spectroscopy)光束線的協助，直接佐證了BFO的晶相與反鐵磁性於光脈衝前後的變化。而有限元分析之熱傳導模擬以及超快動力學結果顯示光致暫態應力脈衝為其相變機制來源，脈衝始於5.2皮秒後，允許高速的資料寫入。這些結果展示了以高速脈衝光調控複雜性氧化物系統之物理性質的可能性，為多功能性的材料的光調控提供了廣泛適用的方法。本研究亦被Advanced Materials選為該期frontispiece封面。
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