Y.W. Rheem

Near-surface magnetic properties and giant magnetoimpedance of Co-based amorphous ribbons

Abstract The study of near-surface local magnetic properties and giant magnetoimpedance (GMI) were carried out on Co 68 Fe 4 Cr 4 Si 12 B 12 amorphous ribbons. The amorphous ribbon was obtained by planar flow casting in air (samples N1). The second amorphous ribbon with the same composition (samples N2) was prepared from the part of the ribbon N1 by planar flow casting in a He atmosphere. Scanning Kerr microscopy showed that the studied samples have strongly distinguishing near-surface magnetic properties and different micromagnetic structure (equilibrium distribution of the magnetization). The magnetic field dependencies of GMI ratio profile in these ribbons were discovered to be also various.

Magnetostatic properties of heterogeneous Co-based amorphous/crystalline phases

Abstract Using the magneto-optical Kerr effect, magnetic hysteresis loops are measured on annealed amorphous Co 66 Fe 4 B 15 Si 15 samples, to characterize the magnetostatic properties of the heterogeneous crystalline/amorphous phases. A gradual change, on microscale inhomogeneous, change of the magnetic properties with respect to thickness is revealed on HCP-Co, FCC-Co crystalline phases near the surface. The inner amorphous phase exhibits an irregular variation of the local magnetic properties, presumably due to the occurrence and distribution of microcrystallites. The effective field, exerted by the crystalline layer on the amorphous phase, is opposite to the surface magnetization, indicating that there is an antiferromagnetic coupling between surface and inner amorphous phases.

Hysteretic characteristics of giant magnetoimpedance due to the exchange coupling in annealed amorphous materials

Experiments of the giant magnetoimpedance (GMI) profile have been performed in annealed amorphous Co66Fe4B15Si15 ribbons in open air to characterize the role of the bias field on the GMI. The GMI ratio profile measured at 0.1 MHz exhibits a drastic step-like change, the so-called GMI valve, in an 8 h annealed sample at 380 °C. The GMI valve is related to exchange coupling of the bias field with magnetization of the soft amorphous phase, where the bias field is caused by hcp-Co and fcc-Co crystalline phases on the surface B and Si depleted layer. The bias field is stable for an external field less than 100 Oe, but its direction is entirely changed according to the external field over 400 Oe. The GMI profile begins to reveal hysteresis for increasing and decreasing cyclic fields when the maximum field strength exceeds 200 Oe. The peak for the increasing field is positioned in the negative field region, but in the positive field region for decreasing field. This behavior is opposite to general magnetic hyste...

The GMI profiles of surface-removed amorphous ribbon

Results are reported on the giant magnetoimpedance (GMI) in soft-magnetic Co-based amorphous ribbons in view of their high potential for magnetic sensor applications. The thickness dependence of the GMI profile has been examined in surface-removed amorphous ribbons. The GMI valve characteristic decreases with increasing frequency, and asymmetric GMI profiles in the as-received state change into symmetrical ones with increasing etching time. The maximum of the GMI ratio, DZ=Z; appears at a frequency of 1 MHz and decreases with increasing frequency. The frequency shift of DZ=Z reveals the dominant process controlling MI effect in the amorphous region. r 2002 Elsevier Science B.V. All rights reserved.

Depth profile of transverse permeability spectrum in an annealed Co-based amorphous ribbon

In this article, we investigate the depth profile of transverse permeability spectra extracted from MI spectra in annealed ribbons under weak magnetic field in order to clarify the effect of crystalline layer on the magnetisation process.

Depth profiles of magnetostatic and dynamic characteristics in annealed Co66Fe4B15Si15 amorphous ribbons

We investigated the magnetostatic and dynamic properties of annealed and etched Co66Fe4B15Si15 amorphous ribbons. The near-surface magnetic characteristics of the annealed samples showed the gradual growth of a hard magnetic layer with increasing annealing time; that is, coercivity Hc and saturation field Hs increase from 15 to 600 Oe and from 45 to 1500 Oe, respectively. On the etching effect on the magnetic property in an 8 h annealed sample, the hard magnetic layer near the sample surface was retained for the sample with etching time tetch<40 s, but the influence of the ribbon core on the near-surface magnetic properties of the sample was discovered for tetch⩾50 s. When the thickness of hard magnetic layer is about 1 μm, the asymmetric giant magnetoimpedance (GMI) profiles, the so-called GMI valve, do not show hysteresis. As the thickness is reduced, a hysteretic GMI is observed due to the cyclic change of magnetization in the hard magnetic layer under a cyclic field.

Separation of circumferential magnetic components from MI spectra in laser-annealed Co-based amorphous microwires

A commercial glass-covered Co-based amorphous microwire (Co/sub 66/Fe/sub 3.8/Ni/sub 1.4/B/sub 11.5/Si/sub 14.6/Mo/sub 1.7/) with metallic core diameter of 17 /spl mu/m was annealed in air by illuminating the pulsed Nd:YAG laser beams under longitudinal and transverse annealing fields, denoted by H/sub l/ and H/sub t/, respectively. The static susceptibilities by domain-wall motion and magnetization rotation, /spl mu//sub dw/ and /spl mu//sub rot/, were separated from the circumferential complex permeability extracted from impedance spectra. The /spl mu//sub rot/ shows a maximum value of the laser-annealed sample with H/sub l/=20 Oe, which indicates the increased volume of axial domain in the core by laser-annealing under longitudinal magnetic field. The /spl mu//sub dw/ shows maximum value at laser-annealed sample with H/sub t/=20, indicating that the volume of axial domain in core is increased by laser annealing under transverse magnetic field.

Giant magnetoimpedance in Co-based microwire annealed by pulsed Nd:YAG laser

The influence of laser annealing on giant magnetoimpedance (GMI) effect of glass-covered Co-based amorphous microwires was investigated by illuminating pulsed Nd:YAG laser beam on the etched microwires. The maximum GMI ratio at 5 MHz under cyclic magnetic field frequency increases from 60% for the as-etched microwire up to 73% and 110% after laser annealing without and with the annealing magnetic field, respectively.

Application of current sensor using asymmetric giant magnetoimpedance in amorphous materials

Summary form only given. In annealed Co-based amorphous samples in open air, giant magnetoimpedance (GMI) exhibits a step-like change as a function of the applied magnetic field, which reveals the excellent sensitivity and linearity for the magnetic field. In this study, we present a GMI DC current sensor using a sample wound in the circular form.

Influence of Annealing Temperature on Magnetic Properties in Co-Based Amorphous Ribbons

The magnetic properties were investigated on Co66Fe4B15Si15 amorphous ribbons of annealed at temperature range from 473 K to 773 K in vacuum (A-batch) and open air (B-batch). Static permeability from domain wall motion decreases with annealing temperature both in A- and B-batch sample. The permeability from magnetization rotation increases up to 700 K annealing temperature, but then decreases. The GMI profiles show a symmetric curve in A-batch samples irrespective of annealing temperature. In B-batch samples, symmetric profiles are shown up to 650 K annealing temperature, while they becomes asymmetric for further annealing temperature, due to the exchange bias-field induced by surface crystalline layer.