铁电基底上CoFe和CoNi薄膜磁特性的电场调控研究

发布时间：2018-10-16 11:37

【摘要】：随着信息技术的高度发展,人们对信息的依赖性越来越强,同时也对信息存储设备提出了更高的要求。目前人们广泛使用的磁信息存储器件利用电流产生磁场改变磁化状态来写入信息,存在写入功耗高的缺点。因此,寻找一种新的更快速、更高效、低能耗的信息写入方式成为磁信息存储领域迫切的要求。本论文中我们研究了铁电/铁磁结构中电场对磁性薄膜磁化状态的调控作用,这种新的调控方式具有热损耗少、所需空间小、电压可定点施加等优点,在将来的磁信息存储器件中有很好的应用前景。我们选择在磁电阻效应研究中被广泛使用的CoFe和CoNi薄膜作为研究材料。研究内容主要包括下面四部分：1)研究了(1-x)[Pb(Mg11/3Nb2/303)]-x[PbTi03] (PMN-30%PT)铁电基底上,电场对CoFe薄膜磁特性的调控效应。由于PMN-30%PT巨大的压电系数和CoFe薄膜优异的软磁性及大的磁致伸缩系数,12kV/cm电场作用下CoFe薄膜产生的各向异性场达到了1.2kOe,对应磁电耦合系数为100Oe cm/kV, CoFe薄膜磁矩发生了90°旋转,面内难易磁化方向发生了互换。2)研究了PMN-30%PT基底上电场对超顺磁性FeCo-SiO2颗粒膜的调控效应。在CoFe-SiO2结构中,当Si02含量为45%时,CoFe表现出很好的超顺磁性。电场作用下PMN-30%PT产生面内各向异性应变,使CoFe磁矩沿应变伸长方向一致排列,CoFe薄膜由超顺磁性纳米颗粒膜变为具有面内单轴各向异性的单畴颗粒膜。3) CoNi薄膜的成分对磁性及磁电阻值有很大的影响,本论文研究了铁电基底PMN-30%PT和PMN-32%PT上,电场对CO43N157和CO23Ni77薄膜磁特性的调控效应。Co23Ni77/PMN-32%PT结构中,电场效应产生的各向异性场达到了4000e,磁电耦合系数达到了40Oecm/kV。由于CoNi薄膜的磁致伸缩系数与CoFe相反,电场对CoNi和CoFe磁矩的调控作用相反。在PMN-PT/(CoFe/Cu/CoNi)n多层膜结构,通过外加电压可实现CoFe与CoNi磁矩由平行态到垂直态的转变,相应的薄膜由低阻态变为高阻态,这种效应可应用于电写磁读信息存储器。4)铁电/铁磁结构中电场对磁性层的调控效应与铁电层的应变特性有很大的关系。PMN-30%PT单晶材料,电场作用产生的面内线性应变大于非线性应变,基于应变调控的磁性变化表现为易失性的Butterfly形状；对于PMN-32%PT单晶材料,由于其极化过程中,71°和109°电极化方向的翻转导致面内有很大的剩余应变效应,CoNi薄膜磁矩随电场的变化表现出非易失性的Loop形状,这种非易失性的调控对实现电场写入信息存储器件有很重要的意义。
[Abstract]:With the development of information technology, people rely more and more on information, and also put forward higher requirements for information storage devices. At present, magnetic information storage devices, which are widely used by people, use current to produce magnetic field to change the magnetization state to write information, which has the disadvantage of high power consumption. Therefore, it is an urgent requirement in the field of magnetic information storage to find a new faster, more efficient and less energy consuming way to write information. In this paper, we study the effect of electric field in ferroelectric / ferromagnetic structure on the magnetization state of magnetic thin films. This new control method has the advantages of less heat loss, less space needed, and the voltage can be applied at a fixed point. In the future magnetic information storage devices have a good application prospects. CoFe and CoNi thin films, which are widely used in magnetoresistance study, are selected as materials. The main contents are as follows: 1) the effects of electric field on the magnetic properties of CoFe thin films on (1-x) [Pb (Mg11/3Nb2/303)] -x [PbTi03] (PMN-30%PT) ferroelectric substrates are studied. Due to the large piezoelectric coefficient of PMN-30%PT and the excellent soft magnetism and magnetostrictive coefficient of CoFe thin film, the anisotropic field of CoFe film under the action of 12kV/cm electric field reaches 1.2 KOe, which corresponds to the 90 掳rotation of the magnetoelectric coupling coefficient of 100Oe cm/kV, CoFe film. The in plane magnetization direction is interchangeable. 2) the effect of electric field on the superparamagnetic FeCo-SiO2 granular film on PMN-30%PT substrate is studied. In the structure of CoFe-SiO2, when the content of Si02 is 45%, CoFe exhibits excellent superparamagnetism. PMN-30%PT produces in-plane anisotropic strain under the action of electric field. The CoFe magnetic moment is arranged along the strain elongation direction, and the CoFe film changes from superparamagnetic nanocrystalline film to uniaxial anisotropic single-domain granular film. 3) the composition of CoNi film has great influence on the magnetic properties and magnetoresistance. The effect of electric field on the magnetic properties of CO43N157 and CO23Ni77 thin films on ferroelectric substrates PMN-30%PT and PMN-32%PT has been studied in this paper. In Co23Ni77/PMN-32%PT structure, the anisotropy field and magnetoelectric coupling coefficient of CO43N157 and CO23Ni77 thin films are up to 4000eand 40Oecm / kV respectively. Because the magnetostrictive coefficient of CoNi thin film is opposite to that of CoFe, the effect of electric field on the magnetic moment of CoNi and CoFe is opposite. In the structure of PMN-PT/ (CoFe/Cu/CoNi) n multilayer film, the magnetic moment of CoFe and CoNi can be changed from parallel state to vertical state by applying applied voltage, and the corresponding film changes from low resistance state to high resistance state. This effect can be applied to write / read information memory. 4) the regulation effect of electric field on magnetic layer in ferroelectric / ferromagnetic structure is closely related to the strain characteristics of ferroelectric layer. PMN-30%PT single crystal material, The in-plane linear strain caused by electric field is larger than that of nonlinear strain, and the magnetic change based on strain regulation shows a volatile Butterfly shape, while for PMN-32%PT single crystal material, the linear strain is larger than the nonlinear strain. Due to the large residual strain effect due to the reversal of 71 掳and 109 掳polarization directions in the polarization process, the magnetic moment of the CoNi film exhibits a non-volatile Loop shape with the change of the electric field. This non-volatile regulation is very important for the realization of electric field writing information memory devices.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2

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