【摘要】：多鐵材料因其多鐵性(鐵電性,鐵磁性,鐵彈性)以及其中蘊(yùn)含的豐富多場耦合效應(yīng)而在自旋電子器件、傳感器、信息存儲器件等新型多功能器件領(lǐng)域有著廣闊的應(yīng)用前景。近年來,隨著對多鐵材料研究的深入,一些基于該類材料的其他物理性質(zhì)也逐漸引起人們的關(guān)注,例如電阻開關(guān)效應(yīng)、鐵電光伏效應(yīng),等等。這些性質(zhì)與多鐵性之間的互相耦合與作用為實現(xiàn)多場物性調(diào)控、探索新奇物理現(xiàn)象、設(shè)計新型多功能器件提供了新的角度與新的可能。本論文就以多鐵材料中具有代表性的鐵酸鉍基薄膜為研究對象,著重研究其在電阻開關(guān)過程中磁性與光伏效應(yīng)的變化,并探索其中的物理機(jī)制。論文的主要研究內(nèi)容與結(jié)果如下:在BiFe0.9Mn0.1O3多晶薄膜樣品中,基于電阻開關(guān)效應(yīng)實現(xiàn)了體系磁性的調(diào)控。我們利用溶膠-凝膠法制備了 BiFe0.9Mn0.1O3多晶薄膜樣品,觀察到薄膜呈現(xiàn)出明顯的電阻開關(guān)效應(yīng)。對薄膜在不同阻態(tài)下的磁性進(jìn)行了測量,發(fā)現(xiàn)在不同阻態(tài)下薄膜的磁性呈現(xiàn)出規(guī)律性變化,即:在低阻態(tài)下飽和磁化強(qiáng)度較大,而在高阻態(tài)下飽和磁化強(qiáng)度明顯降低。高磁態(tài)與低磁態(tài)間飽和磁矩的變化率高達(dá)～40%。進(jìn)一步的研究表明,這種不同阻態(tài)下的磁性變化具有較好的保持性,并且可重復(fù)開關(guān)。通過XPS測試,我們發(fā)現(xiàn)薄膜在阻態(tài)發(fā)生變化時,部分Fe離子的價態(tài)在二價和三價之間變化,這是導(dǎo)致磁性變化的主要原因。隨后的第一性原理計算結(jié)果表明,摻雜Mn離子可在鐵酸鉍晶體的費(fèi)米面附近引入缺陷能級,從而有利于Fe離子價態(tài)的轉(zhuǎn)變。最后,結(jié)合細(xì)絲模型,我們提出了電阻開關(guān)效應(yīng)中磁性發(fā)生變化的物理機(jī)制,即:在電阻開關(guān)過程中,細(xì)絲的形成和熔斷可導(dǎo)致?lián)诫s錳的鐵酸鉍晶體中Fe離子的價態(tài)發(fā)生變化,從而引起體系磁性的變化。這種不同阻態(tài)下的磁性變化為研發(fā)基于多鐵性材料的多態(tài)存儲器件提供了可能。在BiFeO3多晶薄膜中,利用電阻開關(guān)效應(yīng)實現(xiàn)了光伏效應(yīng)的調(diào)控。我們利用溶膠-凝膠法在ITO導(dǎo)電玻璃上制備了 BiFeO3多晶薄膜樣品,薄膜呈現(xiàn)出明顯的電阻開關(guān)效應(yīng)。發(fā)現(xiàn)在電阻開關(guān)過程中,薄膜的光伏效應(yīng)特性發(fā)生明顯變化,在低阻態(tài)下樣品表現(xiàn)出的較小開路電壓,而在高阻態(tài)下則具有較大的開路電壓。我們對其中的物理機(jī)制進(jìn)行了分析,認(rèn)為主要原因是:薄膜在阻態(tài)發(fā)生變化時,其中的導(dǎo)電通道狀態(tài)由于細(xì)絲的形成和熔斷而發(fā)生變化,從而導(dǎo)致薄膜中內(nèi)建電場發(fā)生變化,進(jìn)而影響光生載流子的分離效率,光伏效應(yīng)因而得以改變。這種不同阻態(tài)下的光伏效應(yīng)變化為研發(fā)基于多鐵性材料的多態(tài)存儲器件提供了一種可能的全新途徑。
[Abstract]:Due to its ferroelectric, ferromagnetic and ferroelastic properties and its rich coupling effects, multiferromagnetic materials have a broad application prospect in the field of novel multifunctional devices, such as spin electronic devices, sensors, information storage devices and so on. In recent years, with the development of the research on multi-ferroelectric materials, some other physical properties based on these materials have attracted more and more attention, such as resistance switch effect, ferroelectric photovoltaic effect, and so on. The mutual coupling and interaction between these properties and multi-iron properties provide a new angle and possibility for the realization of multi-field physical property regulation, the exploration of novel physical phenomena, and the design of new multifunctional devices. In this paper, the representative bismuth ferrate thin films in multi-iron materials are taken as the object of study. The changes of magnetic and photovoltaic effects in the process of resistive switch are studied, and the physical mechanism is explored. The main research contents and results are as follows: in the BiFe0.9Mn0.1O3 films, the magnetic properties of the system are controlled based on the resistive switch effect. BiFe0.9Mn0.1O3 polycrystalline films were prepared by sol-gel method and the resistance switch effect was observed. The magnetic properties of the films in different resistance states are measured. It is found that the magnetic properties of the films show regular changes under different resistance states, that is, the saturation magnetization is larger in the low resistivity state and the saturation magnetization in the high resistance state is obviously lower. The change rate of saturation magnetic moment between high magnetic state and low magnetic state is as high as 40%. Further studies show that the magnetic changes in different resistive states have good retention and repeatability. XPS measurements show that the valence states of some Fe ions change between bivalent and trivalent states when the resistance states of the films change, which is the main reason for the magnetic changes. The results of first-principles calculation show that doped Mn ions can introduce defect energy levels near Ferric surface of bismuth ferrate crystals, which is beneficial to the transition of valence states of Fe ions. Finally, based on the filament model, the physical mechanism of magnetic change in the resistance switch effect is proposed. In the process of the resistance switch, the formation and melting of the filament can result in the change of the valence state of the Fe ion in the manganese-doped bismuth ferrate crystal. Thus, the magnetic properties of the system are changed. The magnetic changes in different resistance states make it possible to develop polystate memory devices based on multi-iron materials. The photovoltaic effect is regulated by the resistance switch effect in the BiFeO3 polycrystalline film. BiFeO3 polycrystalline films were prepared on ITO conductive glass by sol-gel method. It is found that the photovoltaic effect of the film changes obviously in the process of resistive switch. The sample exhibits a smaller open circuit voltage in the low resistance state and a larger open circuit voltage in the high resistance state. We have analyzed the physical mechanism, and we think that the main reason is that when the resistance state of the film changes, the state of the conductive channel in the film changes because of the formation and melting of the filament, which leads to the change of the electric field in the film. As a result, the photovoltaic effect can be changed by affecting the separation efficiency of photogenerated carriers. The change of photovoltaic effect in different resistance states provides a new way for the development of polymorphic memory devices based on polyferric materials.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O484.4
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本文編號：2312799