Synchronized Magnetization Oscillations in F/N/F Nanopillars

Current-induced magnetization dynamics in a trilayer structure composed of two ferromagnetic free layers and a nonmagnetic spacer is examined. Both free layers are treated as a monodomain magnetic body with an uniform agnetization. The dynamics of the two magnetizations is modeled by modified Landau-Lifshitz-Gilbert equations with spin-transfer torque terms. By solving the equations simultaneously, we discuss their various solutions in detail. We show that there exists the synchronous motion of two magnetizations among the various solutions; the magnetizations are resonantly coupled via spin-transfer torques and perform precessional motions with the same period. The condition to excite the synchronous motion depends on the difference between the intrinsic frequencies of the two ferromagnetic free layers as well as the magnitude of current.