Isamu Ogasawara

Asymmetrical magneto-impedance effect in torsion-annealed Co-rich amorphous wire for MI micro magnetic sensor

An asymmetrical magneto-impedance (MI) effect in almost zero magnetostrictive amorphous wires is obtained using torsion annealing and then magnetizing with a high frequency current biased with a DC current. A highly sensitive MI characteristic showing a field detection sensitivity of more than 100%/Oe was realized in the wire annealed with 450 turn/m torsion at 500/spl deg/C, inducing a spiral anisotropy. The change of the torsion direction from clockwise to anti-clockwise inverts the asymmetrical MI effect. A sensitive linear field sensor is successfully constructed using a pair of the asymmetrical MI heads without bias coils.

Uniaxial magnetic FeC thin films sputtered onto polymer substrates

Thin films of FeC were deposited onto a polymer substrate by reactive DC magnetron sputtering, using an argon and hydrocarbon gas mixture. The polymer web is wound by a roll coater, and an individual thin film with a constant thickness is piled up by increasing a number of passes UP to a desired thickness. Uniaxial films with Hk=4000 A/m and low dispersion were obtained. The coercive force was a function of thickness; it was Hc=8 A/m for films 0.8 /spl mu/m thick. The easy axis of the uniaxial anisotropy was along the direction transverse to the rolling direction of the polymer web. The origin of the uniaxial anisotropy is the anisotropic thermal shrinkage of the polymer web is discussed by a model.

Dependence of magnetic properties of (Fe/sub 50/Co/sub 50/)/sub 78/Si/sub 7/B/sub 15/ amorphous wire on the diameter

The dependence of the magnetic properties of amorphous wire on the diameter have been investigated. The anisotropy constant, hence the internal stress, of the wire increases with the wire diameter. The size of the pinned reverse domain at the wire end increases with the wire diameter. Domain observation shows that irrespective of the change in the wire diameter, the domain structure basically consists of chevron domain layer sandwiched between the surface maze domain and the inner core domain.

Large Barkhausen discontinuity of Co-Fe-Si-B amorphous films sputtered on polymer substrate

Co-Fe-Si-B films have been prepared using a roll coater and DC magnetron sputtering system onto a polyethylene terephthalate substrate. This thin film exhibited an excellent uniaxial anisotropy introduced by an asymmetric thermal shrinkage of the substrate. Reversal with a single large Barkhausen pulse has been observed in thin film structure 1 mm by 50 mm by 0.65 /spl mu/m. Closure domains have been clearly identified at the film ends. The threshold for the reversal is the coercive force. The reason for reversal with a single Barkhausen jump is that the long narrow film geometry has essentially zero demagnetizing field over most of the film. Once the walls start to move through the center portion of the film, there is nothing to stop them so the reversal proceeds with a single large Barkhausen pulse.

Asymmetrical magneto-impedance characteristics of torsion-annealed Co-rich amorphous wire

It is well known that Co-rich amorphous wires show the remarkable magneto. impedance (MI) effect, which realizes highly sensitive and quick response micro magnetic sensor[l, 21. In the MI effect, the induced wire voltage symmetrically changes with applied magnetic field in the wire-axw direction. Recently, the asymmetrical MI effect of twisted Co-rich amorphous wire was investigated with the applied asymmetncal ac current through the wire. I t is found that the asymmetrical MI characteristics have the advantage fnr the constitution of linear field Nensors withuut bias coi1[3]. In this paper. we report the effect of torsion-annealing on asymmetrical MI characteristics in Co-rich amorphous wires.