Magnetoresistance in silicon based ferrite magnetic tunnel junction

We report magnetoresistance for silicon based magnetic tunnel junction. We used cobalt ferrite & cobalt nickel ferrite as free layer and pinned layer. The magnetoresistance measured at room temperature through silicon by fabricating FM/Si/FM magnetic tunnel junction. Magnetoresistance shows a loop type behavior with 3.7%. We have successfully demonstrated spin tunneling through silicon with ferrite junction that opens the door for potential candidate for spintronics devices. The spin-filtering effect for this double spin-filter junction is also discussed.     

Controlling the demagnetizing field of an in-plane free layer by exchange coupling with a perpendicular multilayer

The demagnetizing field of a Co₅₀Fe₅₀ free layer in an in-planemicron-sized magnetic tunnel junction (MTJ) can be partially compensated by exchangecoupling with a [Co₉₀Fe₁₀/Pt] _N multilayer with perpendicular magnetic anisotropy via a Ru interlayer. The perpendicularanisotropy for N = 5 is optimized for nominal CoFe and Pt thicknessof 0.4 nm and 1.0 nm, respectively. An increase of tunnel magnetoresistance (TMR) from 2%to 75% is observed in MTJs as the free layer thickness, t variesfrom 1.0 nm to 3.0 nm. A phenomenological model is developed to interpret the TMRdependence in terms of the free layer magnetization rotation from in-plane to out-of-planewith decreasing t, a consequence of interlayer exchange coupling with theperpendicular multilayer. We suggest that this strategy could significantly reduce theswitching current density in such MTJs.     

Possible mechanism for tunneling magnetoresistance in La0.9Ba0.1MnO3/Nb-doped SrTiO3 p-n junctions

The observed tunneling magnetoresistance (TMR) effect in La_0.9Ba_0.1MnO₃ (LBMO)/Nb-doped SrTiO₃ (Nb-STO) p⁺-n junctions is investigated and a possible mechanism responsible for the TMR generation is proposed by taking into account the dynamic spin accumulation and paramagnetic magnetization in the Nb-STO layer. Because of carrier diffusion across the dynamic domain boundaries in the Nb-STO layer and spin disordering in the LBMO layer, the tunneling resistance through the junction is high at zero magnetic field. The spin disordering is suppressed upon applying a non-zero magnetic field, which results in the spin-polarized tunneling in this ferromagnetic/depletion layer/dynamic ferromagnetic sandwiched structure and thus the observed TMR effect. The dependence of the TMR effect on the domain size in the LBMO layer, the tunneling current and temperature as well is explained, qualitatively consistent with the experimental observation.     

磁性隧道结Ni80Fe20/Al2O3/Co的研究

用等离子体氧化形成中间绝缘层的方法可重复制备出具有隧道磁电阻（TMR)效应的Ni₈₀Fe₂₀/Al₂O₃/Co磁性隧道结.光透射谱等实验结果表明等离子体氧化能可控制地制备较致密的Al₂O₃绝缘层.样品的TMR比值在室温下最高可达6.0％,反转场可低于800A/m,相应的平台宽度约为2400A/m.结电阻R_j的变化范围从百欧到几百千欧,并且TMR比值随零磁场结偏压增大单调减小. 关键词：     

利用金属掩模法制备钉扎型磁性隧道结

利用金属掩模法和Ir22Mn78合金反铁磁钉扎层，制备了四种钉扎型的Py/Al2O3/Py，Py/Al2O3/Co，Co/Al2O3/Py和Co/Al2O3/Co磁性隧道结，坡莫合金的成分为Py＝Ni79Fe21.例如：利用狭缝宽度为100?μm的金属掩模，直接制备出室温隧穿磁电阻比值为17.2%的磁性隧道结Co/Al2O3/Co，其结电阻为76Ω,结电阻和结面积的积矢为76×10_{4Ωμm2，自由层的偏转场为1114?A/m，并且在外加磁场0.1114A·m-1之间时室温磁电阻比值 关键词： 磁性隧道结 隧穿磁电阻 磁随机存储器 金属掩模}     

Magnetotransport and interdiffusion characteristics of magnetic tunnel junctions comprising nano-oxide layers upon exposure to postdeposition annealing

Magnetic tunnel junction (MTJ) structures based on underlayer (CoNbZr)/bufferlayer (CoFe)/antiferromagnet (IrMn)/pinned layer (CoFe)/tunnel barrier (AlO_x)/free layer (CoFe)/capping (CoNbZr) have been prepared to investigate thermal degradation of magnetoresistive responses. Some junctions possess a nano-oxide layer (NOL) inside either in the underlayer or bufferlayer. The main purpose of the NOL inclusion was to control interdiffusion path of Mn from the antiferromagnet so that improved thermal stability could be achieved. The MTJs with NOLs were found to have reduced interfacial roughness, resulting in improved tunneling magnetoresistance (TMR) and reduced interlayer coupling field. We also confirmed that the NOL effectively suppressed the Mn interdiffusion toward the tunnel barrier by dragging Mn atoms toward NOL during annealing.     

Inverse TMR in a nominally symmetric CoFe/AlOx/CoFe junction induced by interfacial Fe3O4 investigated by STEM-EELS

We have found inverse tunneling magnetoresistance (TMR) with a non-symmetric bias voltage dependence in a nominally symmetric Si (001)/Ag/CoFe/AlO_x/CoFe/IrMn/Ag magnetic tunnel junction after field cooling. The O K edge fine structure extracted from electron energy loss spectroscopy spectrum images taken at the interfaces of junctions with inverse TMR shows a thin, discontinuous Fe₃O₄ layer at the CoFe/AlO_x interfaces. The Fe L_2,3 edge core level shifts are also consistent with those of Fe₃O₄. We find no Fe₃O₄ layer in junctions with normal TMR. We believe this Fe₃O₄ layer is responsible for the inverse TMR.     

Crystallization characteristics of a middle CoFeB layer in a double MgO barrier magnetic tunnel junction

The crystallization characteristics of a middle CoFeB free layer in a magnetic tunnel junction (MTJ) with double MgO barriers were investigated by tunneling magnetoresistance (TMR) measurements of patterned cells across an 8-inch wafer. The MTJ structure was designed to have two CoFeB free layers and one bottom pinned layer, separated by MgO tunnel barriers. The observed resistance showed three types of TMR curves depending on the crystallization of the middle CoFeB layer. From the analysis of TMR curves, coherent crystallization of the middle CoFeB layer with the top and bottom MgO barriers was found to occur non-uniformly: About 80% of the MTJ cells in the wafer exhibited coherent crystallization of the middle CoFeB layers with the bottom MgO tunnel barrier, while others had coherent crystallization with the top MgO tunnel barrier or both barriers. This non-uniform crystallization of the middle CoFeB layer in a double MTJ was also clearly observed in tunneling electron microscopy images. Thus, control of the crystallization of the middle CoFeB layer is important for optimizing the MTJ with double MgO barriers, and especially for the fabrication of double barrier MTJ on a large area substrate.     

Field-and Current-Driven Magnetization Reversal and Dynamic Properties of CoFeB-MgO-Based Perpendicular Magnetic Tunnel Junctions

We report a perpendicular magnetic tunnel junction(p MTJ) cell with a tunnel magnetoresistance(TMR) ratio of nearly 200% at room temperature based on Co Fe B/Ta/Co Fe B as the free layer(FL) and a synthetic antiferromagnetic(SAF) multilayer [Pt/Co]/Ru/[Pt/Co]/Ta/Co Fe B as the reference layer(RL). The field-driven magnetization switching measurements show that the p MTJs exhibit an anomalous TMR hysteresis loop. The spin-polarized layer Co Fe B of SAF-RL has a lower critical switching field than that of FL. The reason is related to the interlayer exchange coupling(IEC) through a moderately thick Ta spacer layer among SAF-RLs, which generates a moderate and negative bias magnetic field on Co Fe B of RL. However, the IEC among RLs has a negligible influence on the current-driven magnetization switching of FL and its magnetization dynamics.     

Intrinsic asymmetries in spin-valves: a tight binding model study

We have calculated the I–V curves, dynamical conductance, and tunneling magnetoresistance (TMR) of 1D magnetic tunneling junction through singleband tight binding model calculations based on the non-equilibrium Green's function approach. The difference in density of state of two ferromagnetic leads and the bias dependence of the propagator cause intrinsic asymmetries in TMR and dynamical conductance at finite bias. Besides, we have displayed that large TMR can be obtained even at high bias for half metallic leads.     

Observation of a tunneling magnetoresistance effect in magnetic tunneling junctions with a high resistance ferromagnetic oxide Fe2⋅5Mn0⋅5O4 electrode

A high resistance ferromagnetic oxide Fe_2⋅5Mn_0⋅5O₄ (FMO) property as a novel spin injector was investigated with a structure of a magnetic tunneling junction (MTJ) composed of FMO/Al-O/Ni₈₀Fe₂₀, in order to reduce an impedance mismatch problem on molecular spintronics. A tunneling magnetoresistance (TMR) effect in the MTJs was observed. The maximum TMR ratio observed in the MTJs was approximately 0.85% at room temperature (RT), and the spin-polarization of FMO was estimated to be at least 0.94% at RT.     

Nanodomain wall film structure and its magnetic characterization

In this letter, we report on a nanodomain wall thin-film structure and its fabrication. The core unit of this structure consists of a magnetic nanodot layer sandwiched between a magnetically free layer and a pinned layer. When the magnetizations of the free layer and the pinned layer are unparallel, a nanodomain wall is formed in the magnetic nanodot. Based on this concept, a nanodomain wall film structure with a Ni/Al₂O₃ nanodot layer is prepared. Since the free and pinned layers are coupled through magnetic nanodots, a displacement of free layer M–H loop from zero field is observed. By measuring the displacement field of the free layer, the nanodomain wall energy is estimated.     

Room-temperature tunnel magnetoresistance and spin-polarized tunneling through an organic semiconductor barrier

Electron spin-polarized tunneling is observed through an ultrathin layer of the molecular organic semiconductor tris(8-hydroxyquinolinato)aluminum (Alq3). Significant tunnel magnetoresistance (TMR) was measured in a Co/Al2O3/Alq3/NiFe magnetic tunnel junction at room temperature, which increased when cooled to low temperatures. Tunneling characteristics, such as the current-voltage behavior and temperature and bias dependence of the TMR, show the good quality of the organic tunnel barrier. Spin polarization (P) of the tunnel current through the Alq3 layer, directly measured using superconducting Al as the spin detector, shows that minimizing formation of an interfacial dipole layer between the metal electrode and organic barrier significantly improves spin transport.     

TMR与GMR传感器1/f噪声的研究进展

隧道结磁阻(TMR) 传感器及巨磁阻(GMR) 传感器的1/f噪声在低频段噪声功率密度较大, 是影响其低频下分辨率和灵敏度的主要噪声形式. 本文详细介绍了近年来TMR传感器及GMR传感器1/f噪声的特点、来源、理论模型、检测方法及降噪措施等方面的研究进展, 并就隧道结磁阻传感器1/f噪声的物理模型进行了详细解释. 通过纳米模拟软件Virtual NanoLab对不同MgO厚度的Fe/MgO/Fe型磁性隧道结(MTJ) 进行了隧穿概率和TMR变化率的模拟计算, 得到保守估计与乐观估计的TMR变化率, 分别为98.1%与10324.55%, 同时通过MTJ的噪声模型分析了MgO厚度对TMR传感器噪声的影响. 制备了磁屏蔽系数大于10000的磁屏蔽筒并搭建了磁阻传感器1/f噪声的测试平台, 通过测试验证了磁屏蔽系统对环境磁场具有较好的屏蔽效果, 为噪声检测提供了稳定的磁场空间. 最后分析了TMR与GMR中各种因素对传感器噪声的影响, 提出了影响MTJ传感器1/f噪声的因素及一些降噪措施.     

Annealing effect on tunneling magnetoresistance in MgO-based magnetic tunnel junctions with FeMn exchange-bias layer

MgO-based magnetic tunnel junctions were fabricated, with a thin pinned CoFeB layer in the unbalanced synthetic antiferromagnet part of the stack FeMn/CoFe/Ru/CoFeB. Inverted and normal tunneling magnetoresistance (TMR) values occur at low and high annealing temperatures (T_a), respectively. The TMR ratio remains inverted up to T_a=300 °C and it becomes normal around T_a=350 °C. The exchange bias of FeMn disappears at high T_a. The sign reversal of the TMR ratio is mainly attributed to the disappearance of the exchange bias due to manganese diffusion during the annealing process.     

Si被注入Gd后的磁性及其整流特性的研究

采用离子束技术，在n型硅基片中注入稀土元素钆，制备了磁性-非磁性p-n结.磁性层Gd_xSi_1-x表现出优良的磁学性能，高居里温度，高原子磁矩(利用RKKY模 型 可以得到解释)，低矫顽力，并保持着半导体的属性，磁性-非磁性p-n结具有整流特性，但 没有观察到明显的磁电阻效应. 关键词： 磁性半导体 磁性p-n结 钆的硅化物 离子束外延     

巨磁电阻材料La0.9Sr0.1MnO3与半导体Si组成的二极管的整流特性

掺杂锰氧化物La_0.9Sr_0.1MnO₃薄膜被直接沉积在n型 硅基片上，构成p-n结.这种p-n结在很宽的温度范围内都有很好的整流特性.研究结果表明， 这种p-n结的结电阻对低磁场敏感，在3×10^-2T的磁场下，磁电阻可达70％.磁 电阻的正负依赖于温度.磁电阻的大小可通过加在p-n结上的电压调节.     

Bias voltage dependence of inverted magnetoresistance on the annealing temperature in MgO-based magnetic tunnel junctions

MgO-based magnetic tunnel junctions (MTJs) with a layer sequence Ir₂₂Mn₇₈ or Fe₅₀Mn₅₀ (10 nm)/CoFe (2 nm)/Ru (0.85 nm)/CoFeB (0.5?t<2 nm)/MgO (2.5 nm)/CoFeB (3 nm) have been fabricated. The bias voltage dependence of tunneling magnetoresistance (TMR) is given as a function of the annealing temperature for these MTJs, which shows the TMR ratio changes its sign from inverted to normal at a critical bias voltage (V_C) when an unbalanced synthetic antiferromagnetic stack CoFe/Ru/CoFeB is used. V_Cs change with the thickness of the pinned CoFeB and annealing temperature, which implies one can achieve different V_Cs by artificial control. The asymmetric V_C values suggest that a strong density-of-states modification occurs at bottom oxide/ferromagnet interface.     

磁性隧道结Ni80Fe20/Al2O3/Co的制备和物性

用等离子体氧化形成绝缘层的方法,重复性地制备出了Ｎｉ８０Ｆｅ２０／Ａｌ２Ｏ３／Ｃｏ磁性隧道结。样品的隧道磁电阻（ＴＭＲ）比值在室温下最高可达６．０％,翻转场（ｓｗｉｔｃｈ ｆｉｅｌｄ）可低于８００Ａ／ｍ,平台宽度约２４００Ａ／ｍ。结电阻的变化范围从几百欧姆到几百千欧。     

具有纳米氧化层的磁性隧道结的热稳定性研究

研究发现在磁隧道结的反铁磁层和被钉扎铁磁层之间插入一层纳米氧化层，可以使磁隧道结的退火温度增加了40℃，即明显地提高了磁隧道结的温度稳定性.通过卢瑟福背散射实验直接观察到产生这一效应的原因是该纳米氧化层有效地抑制了Mn元素在退火过程中的扩散，从而使TMR值在较高的退火温度下得以保持. 关键词： 磁性隧道结 隧穿磁电阻 热稳定性 纳米氧化层