Spin dynamics in small magnetic tunnel junctions

1.利用微细加工技术实现纳米区域的自旋注入(1)利用聚焦离子束(FIB)和电子束光刻技术制备了具有氧化镁势垒的微小磁性隧道结(MTJ)。最小尺寸为100×200 nm^2，电阻x面积积为6Ωμm^2，隧道磁阻比为90%。(2)成功地观察到MTJ的自旋注入磁化反转。电流密度为7.7×10~(-6)A/cm~2，且密度随退火温度升高而增大。(1)测量了铁磁性(FeNi)/非磁性(Cu，Ru，Pt)和FeNi/Cu/Pt多层膜的铁磁共振(FMR)谱，并由FMR谱线宽度估算了自旋弛豫时间和自旋扩散长度。在室温和液氦温度下，铜的自旋扩散长度分别约为350 nm和1000 nm。(2)测量了铁磁/铜/CoFe多层膜的铁磁共振谱，测量了铁磁/铜/CoFe多层膜的铁磁共振线宽增大率。在以CoFeB为调频的情况下，CoFeB的线宽增加，而CoFeb的增加比例较小。利用共面线的快速脉冲场测量响应信号(1)为了对自旋注入磁化反转进行电检测，建立了一套自制的探测装置(脉冲宽度：1μS，最大脉冲电流：20 mA)。测量了脉冲宽度对反转电流的影响。为了在小于500ps的时间尺度上测量自旋动力学，搭建了泵浦-探测测量系统。测量了尺寸为180μm×90μm的坡莫合金的进动信号，得到其阻尼参数α为0.008。(3)合成亚铁磁体的阻尼参数大于FeNi单层薄膜。

1. Spin injection into nano-area by using micro-fabrication technique(1) Small magnetic tunnel junctions (MTJs) with MgO barrier were fabricated by using focused ion beam (FIB) and electron beam lithography. The minimum size was 100 x 200nm^2 and the resistance x area product of 6Ωμm^2 and the tunnel magnetoresistance (TMR) ratio of 90% were obtained.(2) Spin injection magnetization reversal was successfully observed for the MTJs. The current density was 7.7 x 10^6A/cm^2 and the density increased with increasing the annealing temperature.2. Spin relaxation at the interface of junctions(1) Ferromagnetic resonance (FMR) spectra were measured for Ferromagnet (FeNi)/Nonmagnet (Cu,Ru,Pt) and FeNi/Cu/Pt multilayers and spin relaxation time and spin diffusion length were estimated from the FMR line width. The spin diffusion length of Cu was approximately 350nm and 1000nm at room temperature and liquid He temperature, respectively.(2) FMR spectra were measured for Ferromagnet(FM)/Cu/CoFe multilayers and the increasing ratio of FMR linewidth for the FM was measured. In case of CoFeB as the FM, the linewidth of CoFe increased, on the other hand, the increaseng ratio of CoFeB was small.3. Measurement of response signal by a fast pulse field from a coplanar line(1) For the electrical detection of the spin injection magnetization reversal, a homemade probing apparatus (the pulse width : 1μs, the maximum pulse current : 20mA) was set up. The reversal current depending on the pulse width was measured. The current increased with reducing the pulse width.(2) Pump-probe measurement system was set up in order to measure the spin dynamics in the time scale less than 500ps. The precession signal of permaloy of the size of 180μm x 90μm was measured and the damping parameter α of 0.008 was obtained.(3) The damping parameter of synthetic ferrimagnet was larger than that of FeNi single layer film.