Size Effect of Inserted Iron Nanoparticles in the MgO-Based Double Barrier Magnetic Tunnel Junction

The transport properties of stacked CoFeB (1.86)/MgO (0.2)/Fe-nanoparticles ( tFe)/MgO (0.5)/CoFeB(0.6) double barrier magnetic tunnel junctions have been characterized. In this investigation, stacked film is prepared by magnetron sputter system, annealed at 250 ^°, and patterned into a micron-scale device using standard electron beam lithography in conjunction with two-angle ion beam etching. First, the structure, magnetic and electrical properties are examined by using transmission electron microscopy, alternating gradient magnetometers, and lock-in techniques. Stacked film having 1.5 nm lateral size of iron nanoparticles (sample S1) exhibits an in-plane magnetic anisotropy, nonetheless the stacked film having 2 nm lateral size of iron nanoparticles (sample S5) possesses out-of-plane magnetic anisotropy. In addition, the micron scaled S1 device displays not only a normal in-plane magnetoresistance (MR) curve but also an anomalous out-of-plane MR behavior, whereas the S5 device only barely shows magnetic response in the in-plane MR. A hysteresis-free linear region in out-of-plane MR curve has shown field sensitivity of ~ 36 Ω/Oe that is promising for magnetic field sensor applications.