Design of spin-injection-layer in all-in-plane spin-torque-oscillator for microwave assisted magnetic recording.

Graphical abstract Highlights • Introducing a new type of spin-torque-oscillator (STO), all-in-plane STO for MAMR. • All-in-plane STO consisting of Spin-Injection-Layer and Field-Generating-Layer. • Large oscillation cone angle of FGL after magnetization switching of SIL. • Design of SIL for oscillation of FGL at a frequency above 20 GHz. Abstract A new type of spin-torque-oscillator (STO), all-in-plane STO, is introduced for microwave assisted magnetic recording (MAMR) that consist of a spin-injection-layer (SIL) and a field-generating-layer (FGL) with an effective in-plane easy axis due to the shape anisotropy separated with a metallic spacer. In this device, electrons are injected from SIL to FGL while the magnetization of the SIL and FGL is saturated to the out-of-plane by the external magnetic field of ∼1.0 T. Micromagnetic simulations showed that the magnetization direction of SIL can be switched to the opposite direction to that of the applied external magnetic field by the use of spin-transfer-torque. This results in a larger spin accumulation in FGL and its oscillation with a large cone angle at a low bias current density. We designed SIL to reduce the critical current density, J c , required for the magnetization switching of SIL. Materials with a smaller saturation magnetization in SIL reduce J c. Smaller spin polarization of SIL leads to a larger spin accumulation in SIL with an opposite direction to the magnetization, resulting in a reduction of J c. This enables magnetization switching of SIL in small J c followed by oscillation of FGL with frequency above 20 GHz with a large out-of-plane oscillation cone angle of 45–50°. The validity of this finding was studied experimentally by developing STO with two SIL materials, Co 2 Fe(Al 0.5 Si 0.5) Heusler alloy and Fe 67 Co 33 , the former has the B2 crystal structure with a large spin polarization and the latter has the A2 crystal structure with a smaller spin polarization. The magnetization configuration of SIL and FGL in STO with a diameter of ∼60 nm is investigated experimentally based on the field dependent resistance change and the oscillation behavior is discussed based on the micromagnetic simulations. [ABSTRACT FROM AUTHOR]