Spin injection into high quality small magnetic tunnel junctions

点击翻译按钮获取中文摘要

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