Masakatsu Senda

Thin-film magnetic sensor using high frequency magneto-impedance (HFMI) effect

This study reports on the performance of a thin-film magnetic sensor which uses the high frequency magneto-impedance (HFMI) effect. In order to obtain a high sensitivity and a large voltage change ratio (/spl Delta/Vpp/Vpp(0): corresponds to the MR ratio), a strip pattern, a closed magnetic circuit, and a NiFe/SIO/sub 2/ multilayer film structure are adopted for the magnetic films of the sensor. A /spl Delta/Vpp/Vpp(0) of 60-70% is achieved by applying an external magnetic field of several Oe. Moreover there is no hysteresis or no Barkhausen noise in this sensor, which has a magnetic film width of 10 /spl mu/m. In terms of linearity, the sensor exhibits modulation degree (m) of 12% and a total harmonic distortion (THD) of 0.8%. >

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 300 °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.

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.

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.

High frequency measurement technique for patterned soft magnetic film permeability with magnetic film/conductor/magnetic film inductance line

This article describes a new technique in the 1 MHz to 1 GHz range for measuring the permeability of patterned soft magnetic films. An inductance line with a magnetic film/conductor/magnetic film structure makes it possible to measure permeability at frequencies of up to 1 GHz because of the low stray capacitance and high resonance frequency of the electric circuit. The magnetic film pattern is designed so that the demagnetizing field can be ignored, and the absolute permeability value is estimated by analyzing the magnetic circuit. No anomaly, which may be caused by a magnetic charge at the pattern edge or a dimensional resonance, is observed using this pattern. Also, the relative permeability μr′(0) and ferromagnetic resonance frequency fk measured with this technique, are confirmed to be in good agreement with the values calculated from static magnetic properties.

Application of Co‐based amorphous ribbon to a noise filter and a shielded cable

This paper describes the application of a Co‐based amorphous alloy ribbon to a common‐mode noise filter in the 1 MHz–1 GHz frequency range. Its saturation magnetization, and relative permeability were 6000 G and 1450, respectively. The 10‐μm‐thick amorphous ribbon exhibits high loss characteristics. The resistance of a 2‐mm‐diam roll of amorphous ribbon (12.5 mm wide and 30 cm long) increases from 3 Ω at 1 MHz to 50 Ω at 350 MHz. It is confirmed that a filter 1/17th the volume of a conventional (ferrite core) filter exhibits the same noise attenuation. Moreover, the noise emission from a twisted pair cable is greatly reduced without any increase in the cable volume by employing the amorphous ribbon as a shielding material.

High frequency signal response of impedance matched UHF carrier type head

We examined the response to a high frequency signal field of a UHF carrier type thin-film head, which employs a permeability change at UHF. The use of a core/lead/core head element with a multilayer film core and the impedance matching technique made it possible to obtain a large output, a high sensitivity, and a broad bandwidth. We achieved a sensitivity of 4 mV//spl mu/m/spl middot/Oe and a field resolution of /spl sim/10/sup -6/ Oe for a 5 MHz-signal field in the 50 /spl Omega/-matched head. In order to examine bandwidth, we proposed using a leak field from a microstripline as a constant signal field for various frequencies. A 3 dB bandwidth of >100 MHz was estimated from experiment and calculation.

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 300 °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.