Spin injection into high quality small magnetic tunnel junctions

研究了利用聚焦离子束(FIB)辅助化学气相沉积制备微小磁性隧道结(MTJ)的工艺。以沉积的钨作为电极，沉积的碳或钨作为掩膜。结面积为400×400 nm^2的MTJ在室温下的隧道磁阻(TMR)约为30%。建立了一种利用导电式AEM测量微小MTJ的磁阻抗装置。2×0.7μm-2结的磁共振率为29%。测量了铜/氧化铝/FeNi/铜多层膜的铁磁共振谱。FMR和电检测微波共振(EDMR)谱都表明，由于自旋进动产生的自旋电流，自旋被注入到非磁性金属层中。为了对磁化反转进行电检测，自制了探测仪。建立了空气共面探头。使用脉冲发生器来产生小于500…的电流脉冲更多的PS上升时间通过MTJ的上电极。在无硬轴场的情况下，随着场脉冲幅度的增加，磁化强度的转换时间减少到500ps，最高可达100Oe。随着硬轴场的增大，磁化强度转换的时间变短，反转变得明显。用Landau-Lifshitz-Gilbert(LLG)运动方程估算的转变时间与实验测量结果吻合较好。用时间分辨磁光克尔效应(MOKE)测量了NM/FeNi/NM(NM=铜和铂)多层膜的磁化进动。建立了采用脉冲激光、光延迟线、样品与光导开关组合产生脉冲场的MOKE测量系统。成功地观察到了运动磁化强度在时间域中的明显振荡和驰豫。Cu/FeNi/Cu多层膜的Gilbert阻尼常数α与FeNi层厚度无关。而随着FeNi层的变薄，多层膜的α增强。这些实验数据与铁磁共振测得的α符合得很好。较少

A process for fabricating small magnetic tunnel junctions (MTJs) by using focused ion beam (FIB)-assisted chemical vapor deposition was investigated. Deposited tungsten was used as an electrode, and deposited carbon or tungsten was used as a mask. MTJs with a junction area of 400 x 400 nm^2 showed a tunnel magneto-resistance (TMR) ratio of about 30 % at room temperature. An apparatus for MR measurement of small MTJs by using conductive AEM was set up. The MR ratio for the junction with 2 x 0.7 μm-2 was 29%.Ferromagnetic resonance (FMR) spectra were measured for the Cu/Al-oxide/FeNi/Cu multilayers. Both FMR and the electrical detected microwave resonance (EDMR) spectra suggested that the spin was injected into non-magnetic metal layers due to the spin current generated by the spin precession.For the electrical detection of the magnetization reversal, a homemade probing apparatus. using air-coplanar probes was set up. A pulse generator was used to create current pulses with less than 500 … More ps rise time through the upper electrode of the MTJs. The time to switch the magnetization decreased to 500 ps with increasing the field pulse amplitude up to 100 Oe with no hard axis field. The time to switch the magnetization became short and the reversal became clear with increasing the hard axis field. The transition time estimated using Landau-Lifshitz-Gilbert (LLG) equation of motion of the exact experimental conditions agreeded well with the experimental measurements.Magnetization precession of NM/FeNi/NM (NM=Cu and Pt) multilayers was measured by time-resolved magneto-optical Kerr effect (MOKE). The MOKE measurement system equipped with a pulse laser, optical delay lines was set up and samples were combined with photoconductive switch for pulse filed generation. Clear oscillation and relaxation of the magnetization of motion in time domain were successfully observed. Gilbert damping constant α for Cu/FeNi/Cu multilayers was independent of the thickness of feNi. While α for Pt/FeNi/Pt multilayers was enhanced as FeNi layer was thinner. These experimental data were well fitted by LLG-calculation with the same α obtained by ferromagnetic resonance. Less