Noriyuki Kumasaka

Magnetic properties of multilayered Fe‐Si films

The coercivity and permeability of Fe‐Si films can be improved by laminating several layers with either nonmagnetic (SiO2, Al2O3, Al or Mo) or ferromagnetic (Ni, Fe, Co or 20‐wt. % Fe–Ni) spacers. It is also found that films made with soft magnetic laminations have an advantage over nonmagnetic or hard magnetic ones. Such behavior is concluded to be attributed to the smaller grain size, and pinhole or exchange coupling of multilayered Fe‐Si films by observing domain and grain structures.

Magnetic properties and film structures of Fe/C multilayers

The magnetic properties and film structures of Fe/C multilayers (period: 5–50 nm) formed by ion beam sputtering are studied. The coercivity in the easy axis direction is decreased from 380 A/m (=4.8 Oe) to 25 A/m (=0.3 Oe) by reducing the period from 50 to 5 n. The relative permeability increases to a maximum of approximately 3000 with increasing C layer thickness. Cross‐sectional transmission electron microscopy and Auger electron spectroscopy show that Fe layers are clearly separated by C layers, resulting in small Fe crystallites.

Soft Magnetic Properties and Magnetic Anisotropy Dispersions of Fe?Ni/Ni?Fe Multilayered Films

Fe/Ni–Fe multilayered films are formed by the ion beam sputtering method. Their magnetic properties and film structures are examined. As the period of the Fe/Ni–Fe multilayered films is reduced, the Fe crystallite diameter and the magnetic anisotropy dispersion become small and the soft magnetic properties are improved. The Fe/Ni–Fe multilayered film, whose period is 25 nm, displays a coercive force of 90 A/m, a relative permeability of 1900, a saturation magnetic flux density of 1.9 T, and a magnetostriction constant of 8×10-7. It is thought that the reduction of magnetic anisotropy dispersion improves the soft magnetic properties of Fe/Ni–Fe multilayered films.

Fe‐C film formation by dual ion beam sputtering

Fe‐C films are formed by dual ion beam sputtering in which an ion beam irradiates the substrate during film formation. The magnetic properties and film structure of the resulting Fe‐C films are investigated. As the acceleration voltage of the substrate beam increases, C concentration in the Fe‐C films decreases, thereby changing the magnetostriction constant of the film from positive to negative. When films formed at an acceleration voltage of 0, 200, and 400 V are heated at 100, 300, and 400 °C, respectively, the relative permeability of each film reaches a maximum. The Fe‐C film with 8 at. % C has a room‐temperature saturation magnetic flux density of 2.2 T, a relative permeability of 900, and a magnetostriction constant near zero.

Probe‐type thin‐film head for perpendicular recording using multilayered Fe‐Si‐Ru films

The coercivity dependence of read/write and noise characteristics are investigated for the probe‐type thin‐film head using multilayered Fe‐Si‐Ru films and Co‐Cr/Co‐Zr‐Mo double‐layer media. The D50 recording density of 100 kFCI (flux change per inch) and the output of 0.24 μVpp/μm turn m/s are obtained for the medium with the coercivity of 500 Oe. These characteristics are superior to those for conventional ring head (D50=80 kFCI, E1k=0.12 μVpp/μm turn m/s). Further, thin‐film heads have low noise and high overwrite characteristics.

Improvement in Soft Magnetic Properties of Heat-Treated Fe–C/Ni–Fe Multilayers

Ion beam-sputtered Fe-9 at%C/Ni-Fe multilayers are heat treated and the changes in their magnetic properties are examined. Relative permeability increases and coercivity decreases as the heat treatment temperature increases. The mean anisotropy field and magnitude dispersion also decrease with increasing temperature. The (110) plane distance decreases with the heat treatment, showing that compressive stress within the film is released. A film separated from the substrate has a decrease in the mean anisotropy field and magnitude dispersion. Thus, it can be concluded that heat treatment plays an important role in releasing stress.

Fe-C films grown by ion beam sputtering and their magnetocrystalline anisotropy constants

Abstract Fe-C films are grown epitaxially on a GaAs (100) single crystal substrate by ion beam sputtering and the magnetocrystalline anisotropy constants of the Fe-C films are evaluated. The magnetocrystalline anisotropy constant of the obtained Fe film is 40 kJ/m 3 , which is 15% smaller than that reported for bulk Fe. The magnetocrystalline anisotropy constant decreases with the addition of C to Fe, and is 32 kJ/m 3 at a C concentration of 3.9 at%. However, this decrease is not large enough to explain the improvement in soft magnetic properties of Fe film obtained by adding C. This supports the idea that the improvement comes from fine crystallites of Fe-C films.

Changes in Soft Magnetic Properties of Fe and Ni-Fe Films Due to the Dispersion Angle of Sputtered Atoms

Fe and Ni-Fe films are formed by the ion beam sputtering method. Changes in magnetic properties due to the dispersion angle of sputtered atoms are examined. The lowest coercive force and the highest relative permeability are obtained at a dispersion angle of 60-90° . The Fe and Ni-Fe films show preferred orientations of and normal to the film plane, respectively. Good soft magnetic properties are found to be obtained at angles in which the films have strong preferred orientations.

A cross-type amorphous video head

Abstract A cross-type video head composed of cross-shaped amorphous sputtered films and ferrite that can be used with high coercive tapes is described. A three-dimensional magnetic field calculation shows that the cross-type head has a strong recording field and high reproduction efficiency compared to a conventional metal-in-gap head (MIG) or a plate-type head. No large bumps in the output spectrum are observed during recording and reproduction under normal conditions with the cross-type head. The amorphous sputtered film deposited on the inclined plane of the ferrite substrate used for the cross-type head shows a homogeneous structure and high permeability similar to that of a film deposited on a horizontal plane. A cross-type head using a CoNZr amorphous film annealed in a magnetic field under optimum conditions shows excellent recording and reproduction characteristics when used with a high coercivity metal tape.

Perpendicular Recording Characteristics of Eight-Turn Probe Type Thin Film Head

The perpendicular magnetic recording/reproduction characteristics of a perpendicular recording thin film head were compared with those of ring heads, in tests using Co-Cr/Co-Zr-Mo double-layer thin film media. The main pole of the thin film head was a 0.3 ¿m Fe-Si-Ru/Ni-Fe multilayered film. The reproduced output per unit coil turn E1k and the overwrite characteristics were both better for the thin film head, and noise levels were lower. These differences were attributed to the larger magnetomotive force coefficients of the medium recording field for the thin film head.