CoFeB/Pt多层膜的垂直磁各向异性研究

具有垂直磁各向异性的磁性纳米结构是自旋转移力矩器件的重要研究内容, 本文采用反常霍尔效应系统地研究了磁控溅射法制备的[CoFeB/Pt]_n多层膜的垂直磁各向异性. 当CoFeB的厚度小于0.6 nm时, 可以在[CoFeB/Pt]_n多层膜中观察到清晰的垂直磁各向异性, 其垂直磁各向异性强烈依赖于CoFeB和Pt层厚度及多层膜周期数. 当多层膜周期数n ≥ 5时, 出现零剩磁现象. 另外, [CoFeB/Pt]_n多层膜的矫顽力均小于2 kA·m^-1, 有望作为垂直自由层的重要侯选材料应用于垂直磁纳米结构中.     

Co/Ni多层膜垂直磁各向异性的研究

采用直流磁控溅射法在玻璃基片上制备了Pt底层的Co/Ni多层膜样品, 对影响样品垂直磁各向异性的各因素进行了调制, 通过样品的反常霍尔效应系统的研究了Co/Ni多层膜的垂直磁各向异性. 结果表明, 多层膜中各层的厚度及周期数对样品的反常霍尔效应和磁性有重要的影响. 通过对多层膜各个参数的调制优化, 最终获得了具有良好的垂直磁各向异性的Co/Ni多层膜最佳样品Pt(2.0)/Co(0.2)/Ni(0.4)/Co(0.2)/Pt(2.0), 经计算, 该样品的各向异性常数K_eff 达到了3.6×10⁵ J/m³, 说明样品具备良好的垂直磁各向异性. 最佳样品磁性层厚度仅为0.8 nm, 样品总厚度在5 nm以内, 可更为深入的研究其与元件的集成性.     

Pt/GdFeCo/Pt多层膜的磁性和反常霍尔效应研究

亚铁磁材料因具有反铁磁排列的子晶格磁矩而表现出诸多丰富的物理性质,在磁信息存储和逻辑领域具有广阔的应用前景.本文采用磁控溅射方法在热氧化的硅基片上制备了Pt/GdFeCo(t)/Pt多层膜,系统研究了亚铁磁GdFeCo厚度对多层膜的表面形貌、结构、磁性以及反常霍尔效应(AHE)的影响.结构测试表明薄膜表面粗糙度较小,且GdFeCo层为非晶态;实验中利用GdFeCo层厚度可有效控制Gd元素含量,从而调控GdFeCo趋近反铁磁态特性的磁矩补偿点;通过重金属强自旋轨道耦合效应(SOC)和非晶态亚铁磁薄膜面内压应力,实现了良好垂直各向异性(PMA);进一步阐明了亚铁磁薄膜中磁性和反常霍尔效应的内在产生机制以及磁矩补偿点与温度的内在关系.这些结果为构建新一代低功耗自旋电子器件奠定基础.     

垂直磁各向异性L10-Mn1.67Ga超薄膜分子束外延生长与磁性研究

具有超强垂直磁各向异性的L1₀-Mn_xGa薄膜由于其与半导体材料结构及工艺的高度兼容性而受到广泛关注, 其超高垂直磁各向异性能和极低的磁阻尼因子预示着L1₀-Mn_xGa薄膜在高热稳定性自旋电子学器件中将发挥重要作用. 而L1₀-Mn_xGa超薄膜对于降低L1₀-Mn_xGa基垂直磁各向异性隧道结中的磁矩翻转临界电流密度有着重要的意义. 本文采用分子束外延的方法, 在半导体GaAs衬底上成功制备出了一系列不同厚度的L1₀-Mn_1.67Ga薄膜, 厚度范围为1-5 nm. 生长过程中反射式高能电子衍射原位检测以及X射线衍射结果均表明了其良好的单晶相. 磁性测量结果表明, 厚度在1 nm以上的L1₀-Mn_1.67Ga薄膜均可以保持垂直磁各向异性特征, 厚度为5 nm的L1₀-Mn_1.67Ga薄膜的垂直磁各向异性能可达到14.7 Merg/cm³. 这些结果为基于L1₀-Mn_1.67Ga的垂直磁各向异性隧道结在自旋转移扭矩驱动的磁随机存储器等低功耗器件的集成及应用提供了重要的实验支持.     

Pt/La0.67Sr0.33MnO3异质结中的反常霍尔效应

非磁/铁磁异质结构中存在很多有趣的演生现象,特别是,铂/铁磁异质结构中的反常霍尔效应是一个研究热点.采用脉冲激光沉积技术和射频磁控溅射技术制备出具有原子级接触界面的铂/锰酸锶镧异质结,并对异质结的电输运性能进行了系统的研究.实验发现,铂/锰酸锶镧异质结中存在由铂贡献的反常霍尔效应,这是由磁近邻效应诱导铂表现出铁磁性造成的.反常霍尔电阻随着温度的降低而急剧增加,并且在低于40 K时改变符号.反常霍尔电阻随铂厚度的增加而急剧降低,证实了铂的铁磁性起源于异质结界面.此外,异质结在低外加磁场下可能产生了拓扑霍尔效应,这是由异质结界面处的Dzyaloshinskii-Moriya相互作用诱导产生手性磁畴壁结构引起的.上述研究结果为进一步理解非磁/铁磁异质结构中的电子自旋和电荷输运之间的相互作用提供了实验基础.     

分子束外延Mn4N单晶薄膜的反常霍尔效应研究

Mn₄N是立方相的反钙钛矿型晶体,具有显著的亚铁磁性和反常霍尔效应.该文利用等离子辅助分子束外延在MgO(100)衬底上生长厚度为40 nm的Mn₄N(100)单晶薄膜,通过X射线衍射θ扫描和φ扫描,证实外延层的结构符合Mn₄N单晶的空间结构特征;化学态测试结果表明Mn₄N(100)薄膜内部存在Mn⁰、Mn²⁺和Mn⁴⁺等几种价态,其实际化学式为Mn_3.6N,薄膜中存在富余的N元素;电学测试数据表明Mn₄N(100)薄膜具有以电子为载流子的反常霍尔效应(在正磁场中得到负的霍尔电阻率),正常霍尔效应的贡献约占千分之六,其反常霍尔电阻率随着测试温度升高5 K～350 K单调增大,说明温度升高导致电子散射现象加剧.通过对测试数据分析可以推断,在5 K～50 K和50 K～75 K温度范围,反常霍尔效应的来源可分别归结为电子斜散射机制和电子边跳机制.在75 K～350 K这一温度范围内,反常霍尔效应...     

自旋阀中的各向异性磁电阻效应

采用平面霍尔效应测量方法，对Ta(8nm)/NiFe(7nm)/Cu(24nm)/NiFe(44nm)/FeMn(14nm)/Ta(6nm)自旋阀多层膜进行了研究.结果表明，在样品中存在着自由层和被钉扎层之间的各向异性磁电阻的“混合”效应.与通常所采用的磁电阻测量方法相结合，平面霍尔效应的测 量可以给出自旋阀中各向异性磁电阻以及自由层和被钉扎层的磁矩随外场变化的更多信息. 关键词： 自旋阀 各向异性磁电阻 平面霍尔效应     

溶液旋涂法制备BixY3-xFe5O12薄膜的自旋输运特性

钇铁石榴石(yttrium iron garnet,YIG)的自旋输运特性一直是自旋电子学的研究重点之一.Bi作为YIG最常见的掺杂元素,其薄膜Bi_xY_3-xFe₅O₁₂的磁光特性已经被广泛研究.但Bi³⁺取代Y³⁺对YIG自旋输运的影响规律还没有被系统地研究过.本文利用溶液旋涂法制备了不同掺杂比的Bi_xY_3-xFe₅O₁₂薄膜,并研究Bi掺杂对YIG薄膜形貌结构和自旋输运性能的影响.结果表明Bi掺杂没有改变YIG的晶体结构,掺杂比上升令薄膜的吸收强度增大,带隙减小.XPS表明了Bi³⁺和Bi²⁺的存在.Bi掺杂在自旋输运上的调控体现在Bi_xY_3-xFe₅O₁₂薄膜的磁振子扩散长度相比纯YIG薄膜有所减小.同时研究发现Pt/Bi_x...     

磁性薄膜的有效垂直磁各向异性场的全输运测量

采用磁控溅射方法,通过金属掩膜板制备了霍尔棒形状"CoFeB/MgO"体系薄膜样品,其中CoFeB层厚度为1.0nm、1.1nm、1.2nm,利用垂直温度梯度的反常能斯特效应和反常霍尔效应对其相关磁输运特性进行了测量,所得结果可分别等效为常规面内和垂直方向的磁滞回线,并由此获得了薄膜的有效垂直各向异性场.     

磁性多层膜CoFeB/Ni的垂直磁各向异性研究

应用磁控溅射法在玻璃基片上制备了以Pt为底层的CoFeB/Ni多层膜结构样品,通过测试样品的反常霍尔效应研究多层膜的垂直磁各向异性(perpendicular magnetic anisotropy,PMA),对影响多层膜垂直磁各向异性的各因素进行了调制.实验结果表明,多层膜的底层厚度、周期层中各层的厚度及周期数对样品的反常霍尔效应和磁性有重要影响.通过对样品各参数的逐步调制,最终获得了具有良好PMA的CoFeB/Ni多层膜最佳样品Pt(4)/[CoFeB(0.4)/Ni(0.3)]_3/Pt(1.0).经测试计算,该样品的各向异性常数K_(eff)为2.2×10~6erg/cm~3(1 erg/cm~3=10~(-1)J/m~3),具有良好的PMA性能,样品总厚度为7.1 nm,完全满足制备垂直磁结构材料的厚度要求,可进一步研究其在器件中的集成与应用.     

Curie temperatures of Y3Fe5O12/Gd3Fe5O12 superlattices

The magneto-optical Kerr effects (MOKE) of epitaxial Y₃Fe₅O₁₂/Gd₃Ga₅O₁₂ (YIG/GGG) garnet superlattices grown on (1 1 1)GGG previously by pulsed laser deposition (PLD) were measured. A series of superlattices were investigated with the thickness of the ferrimagnetic YIG layer varied from six unit cells to only one unit cell while keeping the Curie paramagnetic GGG fixed at one unit cell. It was demonstrated that the ellipsometric technique employing photoelastic modulators (PEM) is sensitive enough to measure the MOKE signals of these ultrathin oxide samples. The Curie temperatures, determined by MOKE, are fit with a power law, yielding a shift exponent λ = 3.1 ± 1.2.     

Magnetic anisotropy manipulation and interfacial coupling in Sm3Fe5O12 films and CoFe/Sm3Fe5O12 heterostructures

The magnetic anisotropy manipulation in the Sm₃Fe₅O₁₂ (SmIG) films and its effect on the interfacial spin coupling in the CoFe/SmIG heterostructures were studied carefully. By switching the orientation of the Gd₃Ga₅O₁₂ substrates from (111) to (001), the magnetic anisotropy of obtained SmIG films shifts from in-plane to out-of-plane. Similar results can also be obtained in the films on Gd₃Sc₂Ga₃O₁₂ substrates, which identifies the universality of such orientation-induced magnetic anisotropy switching. Additionally, the interfacial spin coupling and magnetic anisotropy switching effect on the spin wave in CoFe/SmIG magnetic heterojunctions have also been explored by utilizing the time-resolved magneto-optical Kerr effect technique. It is intriguing to find that both the frequency and effective damping factor of spin precession in CoFe/SmIG heterojunctions can be manipulated by the magnetic anisotropy switching of SmIG films. These findings not only provide a route for the perpendicular magnetic anisotropy acquisition but also give a further path for spin manipulation in magnetic films and heterojunctions.     

Magnetoresistance of Fe3O4/Au/Fe3O4 and Fe3O4/Au/Fe spin-valve structures

A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe₃O₄ electrodes is presented. Fe₃O₄/Au/Fe₃O₄ spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe₃O₄ layers. By contrast, a negative GMR effect is measured on Fe₃O₄/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe₃O₄/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.     

晶格失配应力对单晶(BiTm)_3(GaFe)_5O_(12)膜磁畴结构的影响

利用液相外延工艺在钆镓石榴石衬底上制得了单晶(BiTm)_3(GaFe)_5O_(12)膜,研究了晶格失配应力对其磁畴结构的影响.研究发现,生长速率越快,膜的晶格常数越大;晶格失配应力可以在一定范围内调整膜的垂直各向异性;随着晶格失配应力由较大张应力逐渐转变为较大压应力,磁畴形状先由磁泡畴转变成迷宫畴,然后转变为过渡态部分弯曲的条状畴,最终转变为整齐排列的条状畴;失配应力同时对畴宽也有影响,膜受到的失配应力越大,畴宽越大.这一实验研究对基于控制晶格失配应力来调控单晶膜的各向异性和磁畴结构有指导意义.     

Optimized growth of compensated ferrimagnetic insulator Gd_3Fe_5O_(12) with a perpendicular magnetic anisotropy

Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic,optical,and microwave devices.Among many different garnets,Gd_3 Fe_5 O_(12)(GdIG) is a representative compensated ferrimagnetic insulator.In this paper,we will study the evolution of the surface morphology,the magnetic properties,and the magnetization compensation through changing the following parameters:the annealing temperature,the growth temperature,the annealing duration,and the choice of different single crystalline garnet substrates.Our objective is to find the optimized growth condition of the GdIG films,for the purpose of achieving a strong perpendicular magnetic anisotropy(PMA) and a flat surface,together with a small effective damping parameter.Through our experiments,we have found that the surface roughness approaching 0.15 nm can be obtained by choosing the growth temperature around 700℃,together with an enhanced PMA.We have also found the modulation of magnetic anisotropy by choosing different single crystalline garnet substrates which change the tensile strain to the compressive strain.A measure of the effective magnetic damping parameter(α_(eff)=0.04 ± 0.01) through a spin pumping experiment in a GdIG/Pt bilayer is also made.Through optimizing the growth dynamics of GdIG films,our results could be useful for synthesizing garnet films with a PMA,which could be beneficial for the future development of ferrimagnetic spintronics.     

Fe3O4纳米粒子对P3HT:PCBM电池的影响

为了提高太阳能电池的性能,研究磁性纳米粒子在外加磁场的作用下对聚合物太阳能电池有源层P3HT:PCBM成膜及太阳能电池性能的影响。本文采用热分解法制备了磁性Fe₃O₄纳米粒子,将不同质量分数的Fe₃O₄纳米粒子掺入到P3HT:PCBM溶液中,旋涂后在外加磁场的作用下自组成膜。通过TEM、XRD对制备的Fe₃O₄纳米粒子进行表征,并利用偏光显微镜、原子力显微镜对成膜质量进行探究。结果表明,采用热分解法制备的Fe₃O₄纳米粒子直径在10 nm左右,在外加磁场作用下,Fe₃O₄纳米粒子对成膜有一定的调控作用。当Fe₃O₄纳米粒子掺杂质量分数为1%时,太阳能电池器件的开路电压增加3.77%,短路电流增加24.93%,光电转换效率提高7.82%。     

Mössbauer effect investigations of Co83Fe17/Au/Co/Au multilayers

[Co₈₃Fe₁₇/Au/Co/Au]_N sputter deposited multilayers displaying a giant magnetoresistance have been investigated. Complementary magnetic measurements were conducted in order to characterize a spin reorientation transition in Co₈₃Fe₁₇ layers sandwiched between Au spacers. The transition from a perpendicular magnetic anisotropy to easy-plane one takes place at the thickness of about 1 nm.     

Magnetic anisotropic properties in Fe3O4 and CoFe2O4 ferrite epitaxy thin films

Epitaxial thin films of Fe₃O₄ and CoFe₂O₄ on MgO (0 0 1) substrates were grown by molecular beam epitaxy at low temperature growth process. Magnetization and hysteresis loop of both films were measured to investigate magnetic anisotropic properties at various temperatures. Anomalous magnetic properties are found to be correlated with crystalline, shape, and stress anisotropies. The Fe₃O₄ film below Verwey structural transition has a change in crystal structure, thus causing many anomalous magnetic properties. Crystalline anisotropy and anomalous magnetic properties are affected substantially by Co ions. The saturation magnetization of Co–ferrite film becomes much lower than that of Fe₃O₄ film, being very different from the bulks. It indicates that the low temperature growth process could not provide enough energy to have the lowest energy state.     

Microstructure and transport properties of YBa2Cu3O7−δ films produced by laser ablation from a BaF2/Y2O3/CuO target

The effects of varying the temperature and duration of the post-deposition anneal in watersaturated oxygen were investigated for YBa₂Cu₃O_7−δ films of varying thickness. The films were produced by laser ablation from pressed powder targets consisting of BaF₂,Y₂O₃, and CuO mixtures. This technique produces superconducting films with a highly textured surface. The films were fabricated on SrTiO₃ substrates and were analyzed with X-ray diffraction, scanning electron microscopy, and temperature dependent resistivity. Critical current density (J_c) measurements were performed in magnetic fields up to 1 T. For film thickness on the order of 900 nm, completely c-axis oriented films were obtained with a 60 min anneal at 850°C. Thinner films required less annealing, either shorter times or lower temperatures, to achieve similar results, indicating that the optimal annealing conditions are dependent on film thickness.     

Mechanism of characteristic shape of resistive transition in Bi2Sr2CaCu2O8 films made by laser evaporation

We measured the temperature dependence of resistivity, (T, H), of Bi₂Sr₂CaCu₂O₈ thin films in magnetic fields. These films have a preferential orientation of the c-axis perpendicular to a surface of the substrate. We could not observe any meaningful anisotropy of the characteristic shape of the resistive transition between two cases of the current flow parallel and perpendicular to the magnetic field in the basal plane. Therefore, it is very difficult to ascribe the broadness to any origin due to the Lorentz force produced by an external current.