Switching properties and dynamic domain structures in double barrier magnetic tunnel junctions

Double barrier magnetic tunnel junctions (DBMTJs) with the layer structures of Ta (5 nm)/Ni₇₉Fe₂₁ (40 nm)/Ir₂₂Mn ₇₈ (10 nm)/Co₇₅Fe₂₅ (4 nm)/Al (1 nm)-oxide/Co₇₅Fe₂₅ (8 nm)/Al (1 nm)-oxide/Co ₇₅Fe₂₅ (4 nm)/Ir₂₂Mn₇₈ (10 nm)/Ni₇₉Fe₂₁ (30 nm)/Ta (5 nm) on Si/SiO₂ wafer were micro-fabricated using a TMR R&D magnetron sputtering system and lithography method. TMR ratios of 30.0% and 22.1%, resistance-area product RS of around 32.0 and 27.5 kΩμm², and free layer coercivity of 201 and 141 Oe at 4.2 K and room temperature (RT), respectively, were obtained for the MTJs with a size of 80×80 μm². Static and dynamic domain structures occur as the DC current increases and magnetization switching properties are simulated based on micromagnetics using the energy minimization method. TMR ratios in DBMTJs that are far lower than the expected theoretical values can be clarified based on micromagnetics simulations due to the vortex domain structures formed in the free layer.