Yasuhiro Nagai

Properties of ion-beam-sputtered Ni/Fe artificial lattice film

This paper reports the results of experimental and analytical investigations into the properties of ion‐beam‐sputtered Ni/Fe artificial lattice films. Through structure analysis, it is known that the Fe layer has poor crystallinity and the Ni layer has a face‐centered‐cubic structure with strong preferred orientation. Additionally, the Ni/Fe lattice film is found to possess good soft‐magnetic properties with lower coercivity less than 1 Oe and uniaxial anisotropy as the lattice period is decreased. The saturation magnetization and magnetostriction are also confirmed to be controlled by changing the lattice period and the thickness of Ni and Fe layers. As a result of the simplest model analysis, the very small magnetostriction obtained in this experiment is thought to be realized by the balance in magnetostriction among Ni, Fe, and Ni‐Fe interdiffusion layers. Furthermore, a good domain structure is observed in the Ni/Fe lattice film with very small magnetostriction.

Magnetic properties of ion‐beam‐sputtered Fe/Co and Fe/CoFe multilayer films

This letter reports on the magnetic properties of Fe/Co and Fe/CoFe multilayer films. A zero magnetostriction is realized by changing the thickness of each layer. In addition, Fe/Co films with high magnetization of more than 2 T and good soft‐magnetic properties of 1.5 Oe coercivity are confirmed. By 300u2009°C annealing, the hard‐axis coercivity in Fe/Co films decreases to 0.8 Oe. Furthermore, a suitable magnetic domain structure for a thin‐film head is confirmed, and the structure is found to be determined by the total magnetostriction.

Magnetic properties of Ni/Fe//SiO2 multilayer film

This paper presents an experimental investigation into the magnetic properties of Ni/Fe//SiO2 multilayer films. An increase in magnetic anisotropy and a decrease in hard‐axis coercivity are observed with decreasing the Ni/Fe layer thickness in Ni/Fe//SiO2 multilayer films. By sandwiching thinner Ni/Fe and 5‐nm SiO2 layers together, relative permeability is tremendously increased to a range of 3500–4500. This permeability improvement corresponds well to the minor loop in the M‐H characteristics. The magnetic domain observation indicates that the domain structure is widely changed, and several 180° and reduced 90° walls exist in the pole tip of thin‐film head patterns. The higher relative permeability of over 3000 and the higher saturation magnetization of 1.7 T are confirmed in the thickness range of 0.1–2.0 μm.

Well-defined uniaxial anisotropy in iron film formed by ion beam sputtering

This paper reports on the results of an experimental investigation into the magnetic properties of iron films formed by ion beam sputtering. Through the iron film formation at various nitrogen partial pressures and substrate angles, nitrogen ion bombardment is found to reduce the coercive force of the magnetic hard axis in addition to inducing uniaxial anisotropy. The decrease in the coercive force corresponds well to the increase in the nitrogen concentration and the anisotropy constant of the α‐Fe‐composed films. The uniaxial anisotropy is confirmed to mainly result from directional ordering rather than crystalline anisotropy. The magnetic properties of the film having well‐defined uniaxial anisotropy are a coercive force of 0.3 Oe, a saturation magnetization of 2.2 T, an anisotropy field of 3.5 Oe, and a permeability of 5000.

Magnetic properties of multilayer films consisting of Fe and nonmagnetic layers

This paper discusses a systematic investigation on the magnetic properties of multilayer films consisting of only Fe and nonmagnetic layers (Al2O3, Cu, C, Si, and Ti). Magnetostriction increases and becomes nearly zero as the Fe layer becomes thinner, regardless of the nonmagnetic species. In Fe/Al2O3 and Fe/Cu multilayer films, the magnetostriction increase is thought to be caused by the change in crystal preferred orientation of the Fe layers. By contrast, in Fe/C, Fe/Si, and Fe/Ti multilayer films, the increase is caused by the balance in positive and negative magnetostriction. Additionally, a low hard‐axis coercivity of approximately 1 Oe and a relative permeability of more than 1000 can be achieved in Fe/Cu, Fe/Al2O3, and Fe/C multilayer films. These soft‐magnetic properties are thought to be caused by the weak crystalline magnetic anisotropy due to small crystal grains and the magnetostatic coupling between Fe layers.

Ion bombardment effect on preferred orientation in Ni–Fe film formed by ion beam sputtering

This paper reports on the results of experimental investigation into the preferred orientation of Ni–Fe film formed by ion beam sputtering. Through experiments concerning ion bombardment and substrate temperature, argon ion bombardment is found to increase the amount of the (111) crystal texture in addition to contributing to the texture orientation itself. In terms of film morphology, the fracture cross section indicates a more obvious columnar structure with the film surface becoming slightly rougher as the amount of argon ion bombardment increases. Conversely, nitrogen and oxygen‐mixed ion bombardment weakens the (111) preferred orientation, and the effect becomes more notable when the ion has a higher energy. On the other hand, although the substrate temperature increase makes the (111) texture better oriented, the amount of the crystal texture becomes smaller due to this temperature increase. Additionally, the observed lattice distortion corresponds well to that estimated by the internal stress.

Properties of Ion-Beam-Sputtered Ni/Fe Artificial Lattice Film

This paper reports the results of experimental investigations into the physical and magnetic properties of Ni/Fe artificial lattice films. Through a structure analysis of Ni/Fe lattice films, it is found that the Fe layer has poor crystallinity and the Ni layer has a face-centered cubic structure with strong preferred orientation. Additionally, it is known that the Ni/Fe lattice film acquires good soft-magnetic properties with small coercivity and uniaxial anisotropy as the lattice period is decreased. Saturation magnetization and magnetostriction are confirmed to be controlled by changing the lattice period and the thickness of Ni and Fe layers.

Primary Ar+ ion bombardment effect on Ni–Fe film composition formed by ion beam sputtering

This paper reports results of experimental and analytic investigations concerning the Ni–Fe film composition formed by ion beam sputtering under various forming conditions. From experiments involving the substrate angle and temperature that had dramatic influence on the Ni–Fe film composition, it is found that the primary Ar+ ion bombardment dominates the composition variation. Also, the Ni fraction in Ni–Fe film and its deposition rate decrease as the ion current density increases. As a result of simple analysis, this composition variation is found to be caused by preferential resputtering. Conversely, the Ni fraction increases as the substrate temperature increases without a deposition rate change under primary ion bombardment. This phenomenon cannot be explained only by preferential resputtering. It also includes the formation of an Fe‐rich layer on the film surface.

Magnetic properties of Fe/Co, Fe/CoFe, and (Fe/Co)/SiO2 multilayer films

This paper reports on the systematical investigation into the magnetic properties of Fe/Co, Fe/CoFe, and (Fe/Co)/SiO2 multilayer films. Magnetostriction in Fe/Co and Fe/CoFe films can be controlled by changing the thicknesses of the layers. The Fe/Co film (10/0.5 nm) shows saturation magnetization of more than 2 T and hard‐axis coercivity of 1.5 Oe for magnetostriction near zero. The hard‐axis coercivity is decreased to 0.8 Oe by 300u2009°C annealing. A magnetic domain structure suitable for a thin‐film head is also established for this film. Additionally, a hard‐axis coercivity of less than 1 Oe, a relative permeability of 2000, and a saturation magnetization of approximately 2 T are achieved in (Fe/Co)/SiO2 film [(15/0.5)/5 nm] with no annealing. A controlled domain structure consisting of extended 180° walls is observed in this film.

Magnetic anisotropy in Ni/Fe artificial lattice film

This paper presents an experimental investigation on the magnetic anisotropy and heat stability in Ni/Fe artificial lattice films. Magnetic anisotropy is found to increase as the lattice period and the Fe layer thickness decrease. The annealing of Ni/Fe films is shown to decrease hard‐axis coercivity to 0.3 Oe. However, annealing at temperatures above 400u2009°C causes an increase in coercivity, perfect alloying of the Ni/Fe film, and recovery of the crystallinity of the Fe layer sandwiched between Ni layers. In the Ni/Fe (2/10 nm) film, very small magnetostriction and large saturation magnetization are maintained up to 350°C. A prototype thin‐film head with a Ni/Fe yoke shows stable conventionally reproduced signals for small write currents, superior overwrite properties, and good heat stability at annealing temperatures below 300u2009°C.