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

H. Sepehri-Amin, W. Zhou, S. Bosu, C. Abert, Y. Sakuraba, S. Kasai, D. Suess, K. Hono

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)361-370
Number of pages10
JournalJournal of Magnetism and Magnetic Materials
Publication statusPublished - 2019 Apr 15
Externally publishedYes


  • Microwave assisted magnetic recording
  • Spin accumulation
  • Spin polarization
  • Spin torque oscillator

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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