Keiichi Nagasaka

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 ...

Demonstration and analysis of high resolution differential read-head

We investigated properties of a differential read-head focusing on resolution, output signal, and bit error rate (BER) through experiments and calculations. We successfully observed particular waveforms of the differential head. The fabricated differential heads showed much higher resolution and better BER than conventional heads. Through measurements and calculations, we clarified that as gap-length (GL) between two spin-valves decreases, the resolution for the differential head increases, but the output signal decreases. Accordingly, the differential head has optimal GL to achieve the best BER. The optimal GL is almost the same as the shortest bit length. We also clarified that a calculated differential head with optimized GL has better BER than a conventional head with a shield-gap length of 20 nm, especially at higher linear density. Therefore, the differential head is one of the candidates for reader structures for high-areal-density hard disk drives.