Tetsunori Koda

Thermally assisted magnetic recording on a bit-patterned medium by using a near-field optical head with a beaked metallic plate

A near-field optical head with a beaked metallic plate was used for writing marks on a Co∕Pd bit-patterned medium with a diameter of 20–25nm and a pitch of 30nm. Magnetic-force-microscope images of the medium show that the magnetizations of single bits were selectively reversed by the head. The light-utilization efficiency (defined as the ratio of the absorbed power in the medium to the incident light power) was estimated from the writing condition used and thermal modeling as about 5%.

Study of high magnetic anisotropy Co∕Pd multilayers for patterned media

We have studied the perpendicular magnetic anisotropy of Co∕Pd multilayers for ultrahigh recording density patterned media. By using Pt as an underlayer, the magnetic anisotropy enhances significantly, which is considered to be due to a magnetostriction by inducing a tensile strain into the Co∕Pd multilayers. A patterned medium using the Co∕Pd multilayers has been successfully fabricated with the diameter of the dots and the distance between the center of the dots measuring 20 and 30nm, respectively. The coercivity of the nanopatterned medium is 9.5kOe.

FePt fct phase ordered alloy thin film prepared by 30-s annealing with fe-o under-layer

Fe-O under-layers formed by reactive sputtering with oxygen were applied as under-layers for c-axis orientation control of FePt ordered alloy thin films. Short time annealing for 30 seconds, using an infrared lamp heater was applied. The FePt ordered alloy thin films with Fe-O under-layers after annealing exhibited excellent perpendicular magnetic properties, high perpendicular anisotropy, highly ordered fct-FePt alloy phase and high c-axis orientation.

Enhancement of exchange coupling for antiferromagnetically coupled media

Antiferromagnetically coupled (AFC) media with CoPt or Co interlayers inserted between a Ru layer and CoCrPtB magnetic layers were prepared in order to enhance the exchange coupling and the thermal stability. The exchange coupling field Hex increased from 0.6 to 4.2 kOe by increasing the thickness of the Co interlayer from 0 to 1 nm. The coupling energy J increases with increasing thickness of the interlayer. The coupling energy J of the AFC media with the interlayer are ten times larger (for 1-nm-thick Co interlayer) and five times larger (for 1-nm-thick CoPt interlayer) than that of the medium without the interlayer. Thermal stability factor KuV/kBT for the media with 1-nm-thick Co and 1-nm-thick CoPt interlayers are about 10% larger than that for the medium without the interlayer. The results suggest that the enhancement of the exchange coupling energy induces the increasing of KuV/kBT in the AFC media.

Cross-sectional control of boron contents and the microstructures of Co/Pd multilayer perpendicular magnetic recording media

The effects of cross-sectional modulated boron segregation on Co/PdB multilayer perpendicular magnetic recording media have been studied. Gradually reduced boron contents from thin PdB seed layer (33 at.%) to the top of the Co(0.2 nm)/PdB (0.8-nm) multilayer (12.5 at.% at the center of the multilayer) were successively achieved and confirmed by the depth-profile of X-ray photoelectron spectroscopy (XPS). Observed magnetic properties and magnetic force microscopy images suggested that this gradient diffusion supports reduction of intergrain exchange coupling and improvement of the magnetic properties. The signal-to-noise ratio over 22 dB was obtained at 450 kFCI in playback tests, in combination with amorphous cobalt boron soft-magnetic underlayer (SUL). It is suggested that these properties are brought by a combination of the dispersed nucleation sites with rich boron content in the initial layer and decreasing boron content during the growth of the multilayer. In addition, this simple medium, which consists of only three elements, Co, Pd, B, for the SUL, the seed layer, and the magnetic layer, has a very unique feature of the dull interfaces, observed by a transmission electron microscope.

FePt ordered alloy thin film prepared by 30 seconds annealing with Fe-O under-layer

An Fe-O underlayer formed by reactant sputtering with oxygen is applied as an under layer for c-axis orientation control of FePt ordered alloy thin film. The layered film is then annealed in vacuum by infrared lamp heater for 30 seconds. The magnetic properties and crystallographic structures of the film are studied by means of resonating sample magnetometer and X-ray diffractometer, respectively. It is found that the Fe-O underlayer induces high perpendicular anisotropy. From this result, it is considered that application of Fe-O underlayer and infrared annealing is a useful technique in producing FePt ordered alloy perpendicular magnetic recording media.

Microstructure and segregation effect of Co/Pd multilayer perpendicular magnetic recording media

In this report, we have investigated addition of boron with modulated contents in depth profile and microstructure by a transmission electron microscopy (TEM) with high annular angle dark field (HAADF) detector to evaluate segregation effect.