Detailed spin transfer switching properties in the nanosecond region for CoFeB/MgO(001)/CoFeB magnetic tunnel junctions are reported. The switching current (IC) was greatly increased in the <10 ns region. This characteristic resembles that of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR), although both the junction geometry and resistance differ from those of a CPP-GMR device. We discussed the switching properties considering the contribution of high frequency loss and the theoretical limitation of the analytical model. Furthermore, we observed real-time switching in the nanosecond region. Using these results, we discuss the spin transfer switching mechanism in the nanosecond region with both adiabatic and thermally activated models.

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We report for the first time that the dynamic magnetic intermediate state (DMI) was observed at a speed of several ns during spin transfer switching for MgO-based magnetic tunnel junctions (MTJs). The DMI was observed as slow resistance oscillation at the center of the parallel to anti-parallel state by single shot time domain measurements. The DMI is observable at certain current amplitudes. The outbreak probability decreases with further current increase. We concluded that the DMI originates from inhomogeneous magnetization behavior. On the other hand, previous single shot time domain measurements have shown only for single-domain-like magnetization behavior.

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