Ferrimagnetic Free Layer Research Articles

High-Frequency Current-Controlled Vortex Oscillations in Ferrimagnetic Disks

Recently it was shown that ferrimagnetic nanodisks support a magnetic vortex state that can oscillate at frequencies up to 30 GHz, suggesting that a ferrimagnetic free layer in a spin-torque-driven nanopillar oscillator would have a significantly higher frequency than the ferromagnetic oscillator. Here theory shows that a nanopillar spin-torque oscillator with a current perpendicular to the ferrimagnetic free-layer will indeed drive high-frequency vortex oscillations. This work indicates that it is feasible to construct ferrimagnetic spin-torque oscillators with frequencies increased tenfold, or more. Moreover, the Oersted field from the current provides enhanced frequency control.

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

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.