Yoshiaki Sonobe

CGC Perpendicular Recording Media With CoCrPt-SiO

We investigated a new class of coupled granular/continuous (CGC) perpendicular media consisting of CoCrPt-SiO2 granular layer with magnetically decoupled small grains. By changing the number of Co/Pd bi-layers in the continuous layer, the degree of exchange coupling can be systematically controlled. The introduction of Co/Pd multilayer improved the nucleation field (Hn) from -570 to -1670 Oe and KuV/kB T values from 67 to 97. Compared to the base granular media, the CGC media had 1 dB gain in signal-to-noise ratio (SNR) as well as 14 dB gain in write-ability (OW). Moreover, the output decay was reduced from -0.11 to -0.035 dB per decade. In CGC approach, a more appropriate strength of exchange coupling can be introduced that yields the significant improvement in both SNR and thermal stability

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Coupled granular/continuous (CGC) perpendicular media with two different continuous layers, a Co/Pd multilayer and a CoCrPtB cap layer, were compared. It was confirmed that both thickness optimized layers functioned well as exchange coupled continuous layers. A Landau-Lifshitz-Gilbert simulation was performed for various grain boundary thicknesses, and the signal-to-noise ratio improvement predicted by the simulation was in good agreement with experiments. The CGC structure was susceptible to side erasure on account of its Stoner-Wohlfarth type magnetic switching, and the recording performance was dominated by the granular layer. Controlling this behavior would enable further improvement in recording density. The benefits of discrete-track media with the CGC structure are discussed. We found that ion irradiation of the CGC media could be effective to create soft magnetic regions in between recorded tracks, which act as guard bands, improving the recording performance.

Alloy as Granular Layer

Discrete track media (DTM) and bit-patterned media (BPM) are being extensively studied as routes to achieve higher density hard disk drives. In the DTM and BPM, it is essential to isolate the data tracks or bits with non-magnetic materials to reduce the magnetic noise from adjacent tracks or bits. In contrast to the conventional procedure of physically etching the media, we attempted to isolate the tracks or bits with soft regions using an area-selective ion irradiation method. We prepared hard and soft nano-composite structures by nanoimprinting, followed by ion irradiation. In this study, we confirmed the magnetic reversal process of the hard and soft regions of the nano-composite structure using magnetic force microscopy (MFM) with various external applied magnetic fields. The analysis of the magnetization reversal process of patterned Coupled Granular Continuous (CGC) films with weak exchange coupling confirmed the validity of this novel approach for the fabrication of DTM and BPM.

Approach to High-Density Recording Using CGC Structure

An embedded servo pattern was fabricated using the ion irradiation method. The servo pattern was analyzed using a spinstand with a flyable read/write head and compared with a conventional medium written by a dedicated servo writer. The embedded servo patterns were clearly detected. The good quality of the servo signal proved the effectiveness of the ion irradiation process. No domain wall noise was observed in the ion-irradiated servo area, indicating the absence of large maze domains. LLG simulations were used to investigate the behavior of written tracks and soft-guard-bands of DTM fabricated by ion irradiation. A conventional continuous medium showed an expansion in the width of written tracks as the continuous layer thickness increased. In DTM, track expansion was prevented by the grooves. According to the simulation results, similar magnetic track widths can be obtained in media with soft-guard-bands as in conventional DTM media with air grooves. The Ku reduction in the grooves should align the magnetization of the irradiated guard band region in-plane to realize a successfully erased guard band.

Magnetization Reversal Process of Hard/Soft Nano-Composite Structures Formed by Ion Irradiation

To increase the areal density of hard disk drives (HDDs), discrete track media (DTM) and bit-patterned media (BPM) are being extensively studied. In the DTM and BPM, it is essential to isolate data tracks or bits. Unlike isolating the data tracks or bits using the conventional procedure involving physical etching, we attempted to isolate the tracks or bits with a soft guard band using an area-selective ion irradiation method. We prepared hard and soft (H/S) patterned films by nanoimprinting followed by ion irradiation. We confirmed the magnetic isolation of tracks and bits using magnetic force microscopy (MFM) images and magnetooptical Kerr effect (MOKE) signals. The results of an analysis of the magnetic properties of patterned coupled granular continuous (CGC) films with weak exchange coupling confirmed the validity of this novel approach for the fabrication of DTM and BPM.

Servo-Pattern and Guard-Band Formation in Perpendicular Discrete-Track Media by Ion Irradiation

Summary form only given The realization of perpendicular magnetic recording critically depends on the reduction of medium noise. The CGC media structure with a continuous layer and a granular layer is a candidate for attaining high SNR. The noise characterization of the CGC double-layered media is described by focusing on the transition jitter and magnetization transition analysis using an MFM. CGC media with three different thickness (1.2, 3.6, 6 nm) of the Co/Pt continuous layer were used in this study. All of them had the same 15 nm granular layer. The plain granular medium was chosen as a reference. A single-pole head was used for writing.

Magnetic Properties of Patterned CGC Perpendicular Films With Soft Magnetic Fillings

In order to shed light on the magnetization reversal mechanism of CGC perpendicular recording media, the authors have carried out investigations of its activation volume, the angular dependence of Hc, cluster size and the physical grain size.

Transition noise reduction in CGC perpendicular media

This paper investigates a new class of coupled and continuous (CGC) perpendicular media consisting of CoCrPt-SiO2 granular layer with magnetically-decoupled small grains. This paper describes the role of inter-granular exchange coupling in the recording performance of CGC media structure.