Spin dynamics in small magnetic tunnel junctions

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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.