Spin transfer torque in MTJs with synthetic ferrimagnetic layers by the Keldysh approach

Ichimura, Masahiko*; Hamada, Tomoyuki*; Imamura, Hiroshi*; Takahashi, Saburo*; Maekawa, Sadamichi

Based on the Keldysh Green's function method within the tight-binding model, the spin transfer torque is analyzed in a magnetic tunnel junction with a synthetic ferrimagnetic (SyF) free layer in the ballistic regime. The spin transfer torque exerted on the magnetizations of ferromagnetic bilayers in the SyF free layer tends to rotate the magnetizations in the same direction as a combined motion of the SyF free layer regardless of the bias direction. This rotation causes a reduction of the critical current for the magnetization switching of the SyF free layer which is consistent with experimental observations.