Nobuhide Aoyama

Magnetization suppression in Co/Pd and CoCrPt by nitrogen ion implantation for bit patterned media fabrication

We propose a bit patterned media fabrication method based on low energy nitrogen ion implantation. Nitrogen ion implantation of fcc-Co/Pd multilayer or hcp-CoCrPt single layer suppresses their magnetizations at room temperature. Ion implantation reduces the Curie temperature from 600 to 400 K (or lower) as a result of lattice expansion and reduced exchange interaction between the magnetic atoms in the magnetic layer. We have made media with magnetic dots of 190 to 30 nm in diameter by nitrogen ion doping through resist patterns. Writing and reading of the signal from individual dots were performed with a commercial perpendicular magnetic recording head.

Fabrication, Magnetic, and R/W Properties of Nitrogen-Ion-Implanted Co/Pd and CoCrPt Bit-Patterned Medium

A method of making a cost-effective bit-patterned medium combining: 1) a pattern imprint; 2) ion doping; and 3) an ashing process is described. The Nitrogen ion was doped to change the magnetic properties of the Co/Pd and CoCrPt magnetic layer. The Nitrogen ion induces surface and lattice, and the exchange coupling strength changes during doping which suppress the magnetization and anisotropy of Co/Pd and CoCrPt magnetic layers. This can be achieved at relatively lower dosages so that a subsequent ashing process creates a smooth surface. The thermal stability of doped film and dot was good for practical applications. Monte-Carlo simulations were used to estimate the lateral ionic distribution within the dot region and compared with magnetic-force microscopy. To demonstrate this technique, areal densities of 134 Gb/in2 on Co/Pd media and 250 Gb/in2 on CoCrPt media are shown.

Optical tunneling effect calculation of a solid immersion lens for use in optical disk memory

A solid immersion lens (SIL) has the advantage of easily decreasing the spot size for high data density in optical recording. To accurately obtain the optical tunneling effect for a high-N.A. SIL, we calculated the optical tunneling beam characteristics, using electromagnetic theory. Tunneling beam spot-size dependence on polarization direction and energy-transfer efficiency are also clearly shown.

Reproduced Dot Image of Nitrogen Ion Implanted Co/Pd Bit Patterned Media With Flying Head

We investigated switching and read/write (R/W) characteristics of head flyable (Co/Pd) multilayer bit patterned media (BPM) fabricated by ion implantation. Two-dimensional (2-D) signal mapping of the dc magnetized media shows a clear image of 134 Gbit/in2dots (60 nm× 80 nm pitch, 28 nm dot size). We performed synchronized writing with individual bits with alternate polarity (ac magnetized) and 2-D mapping of 134 Gbit/in2 patterns. The results substantiated the potential of the fabrication technique. From the read-back signal amplitude, we estimated the effective dot size as 24 nm, slightly smaller than the expected value. We discuss R/W properties and important characteristics such as glide height and magnetic structure of BPM.

Optimization of Pit Depth for Concurrent Read Only Memory?Random Access Memory Optical Disk

We have studied a concurrent read only memory?random access memory (ROM?RAM) optical disk system without laser feedback by optimizing pit depth. When the pit depth was 47 nm (optical depth about 1/11 ?) and the pit width 0.45 ?m, about 8% jitter in both pit and magneto-optical (MO) signals was obtained with a 785 nm wavelength laser diode and 0.55 NA objective lens by employing magnetic-field-modulation (MFM) MO recording. Both pit data and MO data were recorded with eight to fourteen modulation (EFM) code with a minimum mark length of 0.83 ?m and a track pitch of 1.6 ?m and thus the areal density is comparable to 1.3 GB for ?120 mm single sided disk. By the optimization of the pit depth, sufficient system margins for practical use were obtained without laser feed back for the simultaneous reproduction of both pit and MO signals.

High optical efficiency integrated head for use in magneto-optical disk drive

We explain the integrated magneto-optical (MO) head module that contains diffractive optical elements (DOE) and a beam-splitter (BS) with cylindrical surfaces. The optical system for servo signal detection is miniaturized by developing a multi-functional DOE. This system yields precise servo signals, and can eliminate the tracking error signal (TES) and focusing error signal (FES) independently. Power detection system is composed by using a multilevel DOE for high-speed automatic power control (APC). We suppress the distribution of the incidence angle on the BS surface, when divergent light is incident on the BS. It enables our integrated head to increase the coupling efficiency of a collimator without the deterioration of optical characteristics. When we test the head in a MO disk drive, the byte error rate (BER) of 10-6 is achieved. We confirm that this drive has the same commercial level performance for a 1.3 GB MO disk with magnetic super-resolution (MSR) technology.