Seiichirou Takahashi

Effects of substrate temperature and annealing on the magnetic properties of FeN films

The properties of iron nitride (FeN) thin films for high-density recording media prepared by the ion-assisted vapor deposition method have been studied as a function of substrate temperature during deposition. The coercivity shows a decrease with increasing temperature. This could be caused by the disordered growth of the columns and a decrease in the magnetic separation owing to the migration of the paramagnetic phase. Annealing tests shows that the coercivity decreases greatly following treatment above 250 degrees C, owing to the decrease in the paramagnetic component in the FeN films. It is concluded that the shape anisotropy of the obliquely oriented columnar structure and magnetic separation effects due to the paramagnetic components that segregate along each column are the main origin of the high coercivity of FeN films. >

Magnetic properties of Fe-Co nitride thin films

For pt.I see ibid., vol.23, p.3630 (1987). The magnetic properties of Fe-Co nitride thin films prepared by the IVD (ion-assisted vapor deposition) method with normal incidence of metal vapor to the substrate were investigated. It was shown that a suitable amount of Co added to the Fe-N films could improve the perpendicular magnetic properties. The highest H/sub k/ and H/sub c perpendicular to /, 4.2 kOe and 600 Oe, respectively, were obtained for a Co addition of nearly 25 at.%. The improvement could be attributed to the change of the distribution of nitride phases inside each column, which would have an effect on the magnetic separation of the ferromagnetic Fe-Co alloy phase from neighboring phases. The saturation magnetization changed with the Co addition, roughly following the Slater-Pauling curve. This was attributable to the change of magnetic moment in the Fe-Co alloy cluster. >

Video Disk Recorder System Using Magneto-Optical Disk

We have developed a video disk recorder system using a magnetically induced super resolution (MSR) magneto-optical (MO) disk 120 mm in diameter and achieved a user data capacity of 4.1 Gbytes per disk using land/groove recording technology, a laser wavelength of 685 nm, and (1, 7) run-length limited (RLL) code. In this case, track pitch is 0.7 µm and minimum mark length is 0.4 µm. The system can record 125 minutes of moving images encoded using the MPEG2 method. In this paper we describe our high-density magneto-optical recording technology and the video disk recorder system which incorporates magnetic field modulation.

Physical properties of CoFe/IrMn spin-valves prepared using ion beam sputtering with an Xe-H2 mixture gas

Co90Fe10/Cu/Co90Fe10/Ir25Mn75 spin-valves with a Ta seed layer were prepared by ion beam sputtering. Improvements in magnetoresistive (MR) and magnetic properties were obtained by adding H2 to Xe sputtering gas. Specifically, the coercivity in the free Co90Fe10 layer considerably decreased as the H2 flow rate was increased. Furthermore, exchange coupling between the Ir25Mn75 and pinned Co90Fe10 layers became stronger in the preparation under the higher H2 flow rate. X-ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy observations suggest that micro-crystallization of each layer is responsible for improving the MR and magnetic properties.

Steep MR change in NiFe/Cu/Co trilayers

A field sensitivity of about 2%/Oe in magnetoresistance (MR) change has been observed in NiFe(6 nm)/Cu/Co(5 nm) trilayers. The MR change was accompanied with a sharp increase in resistivity before decreasing steeply for increasing fields. Thickness of the Ca spacer layer influenced the sensitivity of MR change. These results suggest an existence of interlayer coupling between the two magnetic layers. An analysis of this MR effect suggests that biquadratic coupling plays an important role in the steep MR change.