电场调控的氧化物与薄膜磁性研究

发布时间：2018-01-05 11:16

本文关键词：电场调控的氧化物与薄膜磁性研究　出处：《山东大学》2017年博士论文　论文类型：学位论文

【摘要】：磁性材料在社会生活与国民经济中具有广泛而重要的作用,随着科学技术的日益发展,越来越多的新型磁性材料被应用于各个领域中。纳米材料具有优异的光学、力学、电学、磁学、催化以及光活性,在新材料的研发方面开辟了一个崭新的研究和应用领域。当磁性物质的粒度进入纳米范围时,纳米微粒的小尺寸效应、量子尺寸效应、表面效应等使得它具备了常规多晶或微晶材料所不具备的磁学特性。伴随着对磁性纳米材料高涨的研究热情以及纳米材料独有的优良特性,磁性纳米材料广泛的用途逐渐被人们所发掘出来。磁性纳米材料被广泛的应用于数据储存,磁共振成像,磁流体以及生物医学等众多方面,并取得了显著的成效。随着现代信息技术的迅猛发展,人们对电子元器件的小型化以及多功能化的需求愈加迫切,这使得人们对多种物理效应集于一体的材料的研究表现出更多的关注和兴趣。电极化和磁极化在材料中相互耦合在一起,可以成为设计下一代多功能电子信息记录器件时的一个额外自由度,已成为当前国际上一个新的研究热点。目前已经在单相多铁性材料以及铁磁与铁电新型复合材料中实现了铁磁性和铁电性相互之间的调控,也就是说能够在外加电场下使材料电极化同时诱导磁极化,或者在外磁场下使材料磁极化的同时诱导电极化,这种性质可实现多态存储并大幅提高存储密度。磁电耦合效应,包含着丰富的物理内容,它们涉及到自旋与晶格或声子之间的耦合、强关联电子体系、多重元激发、电子与电子以及电子与声子间的关联等。磁电耦合效应具有广泛的研究与应用价值。科研工作者对磁电效应进行了大量的理论分析和实验探索,并且在磁电效应的应用方面取得了许多成绩。把磁电效应运用到设计存储器件方面,有望实现理想中的"磁读电写"存取方式。传统的信息器件通过独立运用电子的电荷或者自旋属性制得了性能优良的信息器件。为了制备获得功能更强大的非易失性、高密度、低功耗、数据传送比率可靠、快速的存储器件,人们希望将电荷与自旋同时运用于一个器件上,实现电性能和磁性能的相互调控。通过电场来调控磁性是半导体自旋电子学的热点问题,并已被在多种材料中广范研究。具有电场控制的磁性特性的材料将为实现器件的微型化、多功能化以及超低能耗提供广阔的机遇。如何实现电性质与磁性质之间的耦合协同,以及如何制备得到具有较强磁电耦合作用的材料,并深入理解磁电耦合背后的物理机制是研究磁电耦合材料的重点与关键。本论文的主要研究内容及结论如下:(一):我们用固相烧结法合成了 GdFeO3多晶样品,并研究了外加电场对其剩余磁极化强度的调制作用。我们发现GdFeO3的磁性在室温附近具有补偿温度的特性,其剩磁强烈依赖于磁化历史。当外电场施加到GdFeO3样品上时,不同的剩磁状态将会表现出不同的调制作用。我们认为,外电场不仅通过焦耳热效应影响了样品的磁性质,同时还调制了 Fe3+离子的单离子各向异性以及Fe3+离子之间的DM交换作用从而使GdFe03样品的弱铁磁性发生了改变。(二):我们制备了 Ag/TiO2/Nb:SrTiO3/Ag器件并研究了电场作用下器件中电致电阻与磁性的共调控现象。在Ag/TiO2/Nb:SrTiO3/Ag器件中,我们不仅观察到了 set与reset过程所发生的偶极电致电阻现象,同时还获得了较为显著的电场调控的磁性质。Ag/TiO2/Nb:SrTiO3/Ag器件的偶极阻变过程可能来源于在TiO2/Nb:SrTi03界面附近注入电子的束缚/解束缚过程所产生的对于肖特基势垒的调制作用。我们认为电场控制的磁性调制主要来源于伴随阻变过程而产生的Ti02薄膜中空位的生成与湮灭过程。这种电阻与磁性可以同时调制的器件可以被运用在信息逻辑存储器件中。(三):我们制备了 Ag/HfO2/Nb:SrTiO3/Ag阻变存储器件并在其中发现电场可以同时引导器件的阻变以及铁磁性行为。器件中偶极阻变行为来源于Hf02/Nb:SrTiO3界面处注入电子的捕获以及退捕获过程对肖特基势垒的调控作用。在reset过程中随着负向扫场电压的增大,我们在Ag/HfO2/Nb:SrTiO3/Ag器件中观察到了多值电阻转变的存在。在Ag/HfO2/Nb:SrTiO3/Ag器件中发现的多值阻变效应是与reset过程中HfO2/Nb:SrTiO3界面电子捕获以及退捕获的程度有关。我们同时还证明了电场可以通过控制HfO2薄膜中氧空位的浓度从而控制Ag/HfO2/Nb:SrTiO3/Ag器件的铁磁性。随着最大负向扫场电压的增大,器件的饱和磁矩减小,这是因为部分的氧空位在此过程中消失了。多阻态效应以及电场控制的铁磁性在超高密度存储以及磁逻辑器件的应用中很有潜力。(四):我们制备了Ag/Nb2O5/Pt器件并研究了电场作用下器件中电致电阻与磁性的共调控现象。在Ag/Nb2O5/Pt器件中,我们不仅观察到了set与reset过程所发生的偶极电致电阻现象,同时还获得了较为显著的电场调控的磁性质。Ag/Nb2O5/Pt器件的偶极阻变过程可能来源于活跃的Ag离子移动,在材料中形成导电丝以及断裂的过程。而伴随着阻变产生的电场控制的磁性调制则主要来源于伴随阻变过程而产生的TiO2薄膜中空位的生成与湮灭过程。(五):我们通过用平行板电容器对HfO2/NbSrTiO3和HfO2/MgO样品施加了外部电场,并且在HfO2/NbSrTiO3样品中观察到了电场控制的室温铁磁性变化。我们认为长时间的外部电场所驱动的饱和磁矩的改变主要来源于HfO2/NbSrTiO3界面处氧空位浓度的改变。XPS谱表明外加电场同时也能够影响到HfO2表面的氧空位浓度,从而影响到材料的磁性质。我们在室温下观察到的未掺杂HfO2中电场控制的磁性对于自旋电子学以及磁信息存储都有潜在的价值。
[Abstract]:Magnetic materials have wide and important role in the social life and the national economy, with the development of science and technology, new magnetic materials are increasingly used in various fields. The nano material has excellent optical, mechanical, electrical, magnetic, optical and catalytic activity in the development of new materials has opened up a the new research and application field. When the size of magnetic material into the nanometer range, small size effect of nanometer particles, quantum size effect, surface effect makes it have the magnetic properties of conventional polycrystalline or microcrystalline materials are not available. With excellent characteristics unique to high magnetic nano materials and nano research enthusiasm the use of materials, magnetic nano materials are gradually being excavated. The magnetic nano materials have been widely used in data storage, magnetic resonance imaging, magnetic fluid and biological Medical and other aspects, and achieved remarkable results. With the rapid development of modern information technology, the miniaturization of electronic components and function of the increasingly urgent demand, which makes the research of many physical effects set in one of the materials showed more concern and interest. The electric and the magnetic polarization in the material can be coupled together, design the next generation of multi function electronic information recording device for an extra degree of freedom, has become a new international research hotspot. At present already in multiferroic material and ferromagnetic and Ferroelectric Composite Materials in controlled ferromagnetic and ferroelectric among them, that is to say in the applied field of the material and electrode induced magnetic polarization, or in the external magnetic field and the material and electric magnetic polarization induced polarization, this property can be realized Polymorphic storage and greatly increase the storage density. The magnetoelectric coupling effect, contains rich physical contents, which are related to the coupling between the spin lattice or phonons, strongly correlated electron systems, multiple excitations, electron electron and electron phonon relationship between magnetoelectric coupling effect. With a wide range of research and application. Researchers explored the theoretical analysis and experiments on the magnetoelectric effect, and in the application of magnetoelectric effect has obtained many achievements. The magnetoelectric effect is applied to the design of memory, is expected to achieve the ideal of "electro magnetic read write access mode. The traditional information device through the independent use of electronic charge or spin properties excellent performance is prepared. In order to obtain the information device preparation nonvolatile, more powerful high density, low power consumption, reliable data transfer rate, fast storage device, People want to spin and charge and applied to a device, realize the mutual regulation of electrical and magnetic properties. Through the field to control the magnetic semiconductor spintronics is a hot issue, and has been in a variety of materials in a wide range of research. With a magnetic field controlled material properties for miniature devices. Provide a broad opportunities function and ultra-low energy consumption. How to realize the coupling between electrical properties and magnetic properties of coordination, and how to be prepared with strong magnetoelectric coupling effect of materials, and in-depth understanding of the physics behind the magnetoelectric coupling mechanism is the key of magnetoelectric materials. The main research contents and conclusions of this paper are as follows: (a): we synthesized GdFeO3 polycrystalline samples by solid phase sintering method, and studied the modulation effect of external electric field on the residual magnetic polarization. We found the GdFeO3 magnet With the characteristics of temperature compensation in the vicinity of room temperature, the residual magnetism is strongly dependent on the magnetic history. When the external electric field is applied to the GdFeO3 sample, the remanent state will be different show different modulation effects. We believe that the external electric field not only through the Joule heat effect of magnetic properties of the samples at the same time, between the single ion anisotropy Fe3+ DM ion and Fe3+ ion exchange so that the weak ferromagnetic GdFe03 samples changed the modulation. (two) our Ag/TiO2/Nb:SrTiO3/Ag device were investigated under the action of electric field devices in electric resistance and magnetic properties of CO regulated call phenomenon. In Ag/TiO2/Nb:SrTiO3/Ag devices, we not only observe what happened set and reset dipole electroresistance phenomenon, and also won the dipole resistance magnetic properties of.Ag/TiO2/Nb:SrTiO3/Ag devices, electric control is a significant change of the process can be From the injection for Schottky barrier modulation of electron bound / solutions of bound process produced in the TiO2/Nb:SrTi03 near the interface. We believe that the generation and annihilation of vacancies Ti02 thin film magnetic modulation electric field control mainly originates from the resistance change process produced by the process. This kind of magnetic resistance and can simultaneously modulation device can be used in the logical information memory device. (three): we prepared Ag/HfO2/Nb:SrTiO3/Ag resistance memory variable and found that the electric field can also guide device resistance and a ferromagnetic behavior in which devices. The dipole resistive behavior stems from the interface of Hf02/Nb:SrTiO3 injected electron capture and capture back role on the Schottky barrier. In the process of reset with negative field sweep voltage increases, we in Ag/HfO2/Nb:SrTiO3/Ag devices were observed in the presence of multiple resistance transition value. Many values found in the Ag/HfO2/Nb:SrTiO3/Ag device interface HfO2/Nb:SrTiO3 electron capture resistive effect is associated with the reset process and the degree of return capture. We also proved that the magnetic field can by controlling the concentration of oxygen vacancies in HfO2 films so as to control the Ag/HfO2/Nb:SrTiO3/Ag device. With the maximum negative field sweep voltage increases, the saturation magnetization device this is because of the decrease of oxygen vacancies in the process part of the disappeared. Multi resistance state effect and magnetic field control has a potential application in ultra high density storage and magnetic logic devices. (four) our Ag/Nb2O5/Pt device were investigated under the action of electric field devices in Electric Co regulation due to resistance and magnetic phenomena. In Ag/Nb2O5/Pt devices, we not only observe what happened with set reset of dipole electroresistance phenomenon, but also get more The magnetic dipole resistance properties of.Ag/Nb2O5/Pt devices, the electric field significantly variable process may be derived from the Ag ion movement active, forming process of conductive wire and fracture in the material. And annihilation of TiO2 films with vacancy generated magnetic field controlled resistive modulation produced mainly came from with resistive processes arising in the process. (five): we use the parallel plate capacitor application of an external electric field on HfO2/NbSrTiO3 and HfO2/MgO samples, and observed the change of the field control room temperature ferromagnetism in HfO2/NbSrTiO3 samples. We think that the change of saturation magnetization driven by an external electric field of the long time comes mainly from the interface of HfO2/NbSrTiO3 oxygen vacancy the change of the concentration of.XPS spectra show that the electric field can also affect the concentration of oxygen vacancy on the surface of HfO2, which affects the magnetic properties of materials. We observed at room temperature. The magnetic field controlled magnetic properties in the undoped HfO2 are of potential value for spintronics and magnetic information storage.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O484.43;TB383.1

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