Kenji Sugiura

Experimental feasibility of spin-torque oscillator with synthetic field generation layer for microwave assisted magnetic recording

We investigated the oscillation characteristics of a fabricated spin-torque oscillator (STO) with a synthetic field generation layer (FGL) composed of the FGL and perpendicular anisotropy magnetic layer in microwave assisted magnetic recording (MAMR). The fabricated STO was composed of a perpendicularly magnetized reference layer/interlayer/synthetic-FGL. The STO with synthetic-FGL showed very narrow peaks caused by spin-torque oscillation. We also found oscillating frequency of the fabricated STO increased as the external field increased. This implies that the FGL magnetization rotates out-of-plane. Calculations by micromagnetic simulation were qualitatively consistent with the STO measurements. The calculated magnetization configurations in the synthetic-FGL formed a single domain but the one in the single-FGL formed multiple domains. This is one reason that the synthetic-FGL is estimated to generate a larger ac-field. In sum, we experimentally confirmed the effective oscillation of fabricated STO with ...

Thin Spin-torque Oscillator With High AC-Field for High Density Microwave-Assisted Magnetic Recording

A spin-torque oscillator (STO) with perpendicularly magnetized reference layer and a field generating layer (FGL) with high saturation moment was compared with an STO having a perpendicular anisotropy layer (PL) on the FGL using micro-magnetic simulation. The STO without PL was more suitable for obtaining areal-density over 5 Tb/in2 from the viewpoint of achieving a high ac magnetic field and thin stack thickness required for an MAMR head. The FGL stayed in-plane against a strong trailing gap field, and stable high-frequency oscillation was achieved over 10 kOe of perpendicular external field. Magneto-resistance measurement with high applied current was carried out in order to distinguish the stable oscillation with large FGL oscillation trajectories. Qualitative correspondence between the simulation and the experimental results indicated that stable oscillation with large FGL oscillation trajectories was realized in the structure without PL.

Oscillation Stability of a Small Size Spin Torque Oscillator for MAMR

Oscillation behavior of a spin torque oscillator (STO) less than 40 nm in size was investigated by using micromagnetic simulations for microwave-assisted magnetic recording (MAMR) over 5 Tb/in². Decreasing the STO size from 40 to 20 nm deteriorates the stability of a reference layer (REF) and it shrinks the stable oscillation region of a field generation layer (FGL). Enhancing the magnetic anisotropy energy of the REF K_{u_REF} stabilizes the magnetization motion of the REF against the spin transfer torque (STT) effect and the external magnetic field H_z, and the stable oscillation region of the FGL expands within a relative lower applied voltage V_sto region, but random oscillation with fluctuating elevation angles appears at a higher H_z and V_sto. Similar phenomenon is observed when increasing the thickness of the REF t_REF. Enhancing both K_{u_REF} × t_REF and the thickness of FGL are found to stabilize oscillation of the FGL against the STT effect from a stable REF at a larger strength of H_z and a higher V_sto without the appearance of random oscillation, making it possible to apply about 20-nm-square STO to a magnetic head for over 5 Tb/in².