铁酸铋基薄膜阻变特性及其磁性和光伏效应的调控研究
发布时间：2018-11-05 17:33
【摘要】：多铁材料因其多铁性(铁电性,铁磁性,铁弹性)以及其中蕴含的丰富多场耦合效应而在自旋电子器件、传感器、信息存储器件等新型多功能器件领域有着广阔的应用前景。近年来,随着对多铁材料研究的深入,一些基于该类材料的其他物理性质也逐渐引起人们的关注,例如电阻开关效应、铁电光伏效应,等等。这些性质与多铁性之间的互相耦合与作用为实现多场物性调控、探索新奇物理现象、设计新型多功能器件提供了新的角度与新的可能。本论文就以多铁材料中具有代表性的铁酸铋基薄膜为研究对象,着重研究其在电阻开关过程中磁性与光伏效应的变化,并探索其中的物理机制。论文的主要研究内容与结果如下:在BiFe0.9Mn0.1O3多晶薄膜样品中,基于电阻开关效应实现了体系磁性的调控。我们利用溶胶-凝胶法制备了 BiFe0.9Mn0.1O3多晶薄膜样品,观察到薄膜呈现出明显的电阻开关效应。对薄膜在不同阻态下的磁性进行了测量,发现在不同阻态下薄膜的磁性呈现出规律性变化,即:在低阻态下饱和磁化强度较大,而在高阻态下饱和磁化强度明显降低。高磁态与低磁态间饱和磁矩的变化率高达～40%。进一步的研究表明,这种不同阻态下的磁性变化具有较好的保持性,并且可重复开关。通过XPS测试,我们发现薄膜在阻态发生变化时,部分Fe离子的价态在二价和三价之间变化,这是导致磁性变化的主要原因。随后的第一性原理计算结果表明,掺杂Mn离子可在铁酸铋晶体的费米面附近引入缺陷能级,从而有利于Fe离子价态的转变。最后,结合细丝模型,我们提出了电阻开关效应中磁性发生变化的物理机制,即:在电阻开关过程中,细丝的形成和熔断可导致掺杂锰的铁酸铋晶体中Fe离子的价态发生变化,从而引起体系磁性的变化。这种不同阻态下的磁性变化为研发基于多铁性材料的多态存储器件提供了可能。在BiFeO3多晶薄膜中,利用电阻开关效应实现了光伏效应的调控。我们利用溶胶-凝胶法在ITO导电玻璃上制备了 BiFeO3多晶薄膜样品,薄膜呈现出明显的电阻开关效应。发现在电阻开关过程中,薄膜的光伏效应特性发生明显变化,在低阻态下样品表现出的较小开路电压,而在高阻态下则具有较大的开路电压。我们对其中的物理机制进行了分析,认为主要原因是:薄膜在阻态发生变化时,其中的导电通道状态由于细丝的形成和熔断而发生变化,从而导致薄膜中内建电场发生变化,进而影响光生载流子的分离效率,光伏效应因而得以改变。这种不同阻态下的光伏效应变化为研发基于多铁性材料的多态存储器件提供了一种可能的全新途径。
[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.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O484.4
，
本文编号：2312799
[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.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O484.4
，
本文编号：2312799
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