| 研究実績の概要 |
Microwave assisted magnetic recording (MAMR) is a promising technology to overcome the stagnated areal density increase of hard disk drives (HDD). However, its most essential part, “spin-torque-oscillator (STO)”, has not been realized. The STO device for MAMR should oscillate at a frequency>20 GHz at a small current density. We have succeeded in development of a novel STO that oscillates with a frequency above 20 GHz with a small current density. This was obtained by conducting fundamental studies to design the STO by advanced micromagnetic simulations resulting in demonstration of a new design of STO, so called all-in-plane (AIP)-STO, consisting of a spin-injection-layer (SIL) and a field-generating-layer (FGL) separated with a metallic spacer. The designed STO by advanced simulation was fabricated experimentally. Conventional method to analyze the magnetization dynamics using high-frequency electrical signal could not be applied since both FGL and SIL oscillates simultaneously in AIP-STO. We solved this problem by developing a new analysis method using injection locking to an external microwave field. The second fold of this research is design and development of media material for next generation recording technology. We developed TEM image based micromagnetic simulator for high throughput evaluation of nanodefects and micromagnetic parameters of the recording media. Our achievements had a great impact not only in academia but also in the HDD industries toward development of next generation HDD with increased areal density.
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