Giant Magnetoimpedance Ratio Research Articles

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, Δ Z/ Z, appears at a frequency of 1 MHz and decreases with increasing frequency. The frequency shift of Δ Z/ Z reveals the dominant process controlling MI effect in the amorphous region.

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

The study of near-surface local magnetic properties and giant magnetoimpedance (GMI) were carried out on Co 68Fe 4Cr 4Si 12B 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.

Optimization of giant magnetoimpedance in Co-rich amorphous microwires

The dependences of the magnetoimpedance ratio /spl Delta/Z/Z of soft magnetic Co/sub 67/Fe/sub 3.85/Ni/sub 1.45/B/sub 11.5/Si/sub 14.5/Mo/sub 1.7/ glass-coated amorphous microwires with various geometric ratio /spl rho/ upon axial magnetic field H has been measured for the frequency f range 0.06-15 MHz, driving current amplitude I of 0.75-2 mA, and H up to 2400 A/m. Surface hysteresis loops have been measured by transverse magnetooptical Kerr effect (MOKE). A maximum relative change in the giant magnetoimpedance (GMI) ratio /spl Delta/Z/Z up to around 615% is observed at f=10 MHz and I=0.75 mA in the sample with /spl rho//spl ap/0.98. Application of dc bias current strongly affects the GMI ratio. A maximum of GMI ratio occurs approximately at the same field as the coercivity of surface loops.

Giant magnetoimpedance effect and magnetoelastic properties in stress-annealed FeCuNbSiB nanocrystalline wire

Stress-current annealing performed on Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 13.5/B/sub 9/ amorphous wire results in ultra-soft nanocrystalline wire with an additional very homogeneous transverse magnetic anisotropy. The giant magnetoimpedance (GMI) response of this treated wire has been investigated in a range of ac current (I/sub ac/ = 0.2 to 20 mA) and frequency (f = 0.01 to 1 MHz). A maximum GMI ratio as high as around 150% is reported. The magnetoelastic behavior and in particular the influence of applied tensile and torsional stresses, has been analyzed in connection with GMI. From the applied stress dependence of the static field H/sub m/ at which the maximum impedance is observed, the values of induced anisotropy field (H/sub ind/ = 3.46 and 3.14 kA/m) and magnetostriction (/spl lambda//sub s/ = 1.42 and 1.59 /spl times/ 10/sup -6/) are determined.

Giant magnetoimpedance in trilayer structures of patterned magnetic amorphous ribbons

We have measured the giant magnetoimpedance (GMI) and giant magnetoresistance (GMR) of Metglas®/Cu/Metglas trilayer stacks of micropatterned amorphous magnetic Metglas 2714a ribbons and Cu foils. We obtain room-temperature GMI ratios [Z(0)−Z(Hs)]/Z(Hs) up to 800%, and GMR ratios [R(0)−R(Hs)]/R(Hs) up to 2400% at frequencies of 100 kHz–10 MHz, with Hs the magnetic field in which impedance and resistance saturate towards their minimum values. These high values are a direct consequence of the large dynamic relative permeability of the magnetic ribbons and the chosen trilayer geometry. We analyze our results in the context of a theoretical model of L. V. Panina and K. Mohri [Sens. Actuators A 81, 71 (2000)].

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 hysteretic characteristics, suggesting that there is an antiferromagnetic coupling of the bias field with magnetization of the inside amorphous phase.

Magnetic properties and giant magneto-impedance effect study of Fe-based nanocrystalline powder

The macroscopic and microscopic magnetic properties for amorphous and nanocrystalline Fe73.5Cu1Nb3− Si13.5B9 powder have been investigated and their giant magneto-impedance (GMI) effect is reported for the first time. The experimental results show that powder sample annealed at 510°C possesses the optimum soft magnetic properties. However, the maximum longitudinally driven GMI (LDGMI) ratio (about 52%) is found in the sample annealed at 600°C. This means that the LDGMI ratio depends on not only their magnetic properties but also their electric properties.

Giant magnetoimpedance of chemically thinned and polished magnetic amorphous ribbons

We have measured the giant magnetoimpedance (GMI) of microstructured Co-based Metglas® 2714a amorphous magnetic ribbons. Before micropatterning, the amorphous ribbons were chemically thinned or polished, to study the influence of sample thickness and surface state on the GMI effect. The magnetic domain structure of polished foils near saturation is observed using the bitter fluid technique. The well-defined geometry of the samples allows a quantitative comparison of the GMI effect with a simple skin depth model, from which we obtain the frequency-dependent permeability of the material. We have measured the GMI effect for magnetic fields parallel and transverse to the long axis of the sample. We compare the different measurement geometries and film preparation methods and, typically, find a room-temperature GMI ratio of about 35%–90% in fields of a few mT and at frequencies of 10–40 MHz.

Giant magneto-impedance effect in CoMnSiB amorphous microwires

The giant magneto-impedance (GMI) ratio, Δ Z/ Z=[( Z( H)− Z( H max)]/ Z( H max), in a nearly zero magnetostrictive Co 68.5Mn 6.5Si 10B 15 amorphous microwire has been investigated for the frequency range 0.5–10 MHz, driving current amplitude of 0.5–2.5 mA, bias DC magnetic field up to 2400 A/m and under applied tensile stress up to 132 MPa. A maximum relative change in the GMI ratio up to around 130% is observed at a frequency of 10 MHz, magnetic DC field of about 180 A/m, driving current amplitude of 1 mA and under tension of 60 MPa. The tensile stress dependence of the magnetic field, H m, corresponding to the maximum Δ Z/ Z ratio allows to estimate the magnetostriction constant ( λ s≈−2×10 −7) to be in good agreement with λ s values estimated by different methods and in amorphous alloys with similar compositions.

Bias-current effect on giant magnetoimpedance in Co-based amorphous microwire

The giant magnetoimpedance (GMI) effect has been measured in Co 83.2B 3.3Si 5.9Mn 7.6 amorphous microwire as a function of direct current (dc)-biased current and measuring frequency, f. The GMI profile has a single peak for f⩽5 MHz, and two peaks at higher frequency. The maximum GMI ratio increases continuously with frequency up to 45% at 10 MHz. The influence of superimposed dc biasing is shown to result in asymmetrical GMI as well as in a shift of the axial hysteresis loop. Both effects are interpreted in terms of the relative contribution of domain wall and rotational processes to the transverse susceptibility.

Laser annealing effect of giant magneto-impedance in amorphous Co 66Fe 4Nib 14Si 15 ribbon

The magneto-impedance (MI) profiles of Co 66Fe 4NiB 14Si 15 amorphous ribbon varied sensitively with the annealing energy of the pulsed Nd:YAG laser, reflecting the change of anisotropy field which determines the field dependence of transverse permeability. Laser annealing effect of giant magneto-impedance (GMI) in amorphous Co 66Fe 4NiB 14Si 15 ribbon are discussed in terms of laser annealing energy. The pulsed Nd:YAG laser was pumped with Kr-lamp and consisted of a Nd:YAG rod of φ 5 mm×70 mm (AR coated plane/plane), a full mirror and output coupler (30% transmission). The wavelength was 1.064 μm and the pulse width was 220 μs. The GMI ratio increases with annealing energy showing largest value at 136 mJ/pulse (peak power is ∼620 W). The GMI ratio decreases with further increment of annealing energy. The decreasing H k with the annealing energy is ascribed to the increase of magnetic softness, while the increasing H k and the decreasing MI ratio for the further increment of annealing energy could be due to the microstructural change by the laser annealing.

Influence of annealing on the magnetic properties and magneto-impedance response in Fe 84Zr 7B 8Cu 1 ribbons

X-ray diffraction and magnetic measurements have been used to study the structural and magnetic changes produced by annealing Fe 84Zr 7B 8Cu 1 amorphous ribbons at the temperature range 723–923 K for 20 min. Heat treatment causes a devitrification of the amorphous phase giving rise to nucleation and growth of b.c.c. α-Fe phase. Structural and compositional changes result in the amelioration of soft magnetic properties. The giant magneto-impedance (GMI) ratio Δ Z/ Z (Δ Z/ Z=( Z( H)− Z( H max))/ Z( H max)) is enhanced with the devitrification and reaches the maximal value of about 260% at frequency f=6.5 MHz for the ribbon annealed at 873 K for 20 min. The dependence of strong GMI response on frequency and applied field is related to the superior soft magnetic properties of the annealed samples. The sensitive drop of transverse permeability is the source of MI effect through skin effect.

Giant magnetoimpedance in layered FeSiB/Cu/FeSiB films

The giant magnetoimpedance (GMI) effect has been studied in layered FeSiB/Cu/FeSiB films in the frequency range of 100 kHz–40 MHz. The field dependence of the GMI ratio shows that the GMI ratio increases with magnetic field Ha, reaching a positive maximum value at a certain field, and then gradually decreases to negative values. For the layered films with a Cu film width of 0.6 mm, the positive maximum GMI ratio is about 2%, which is smaller than the value of the negative GMI ratio (−6.6% at Ha=50 Oe) at a frequency of 5.2 MHz. With an increase of the Cu film width, a positive maximum GMI ratio of 4.5% and 13.5% is obtained for Ha=30 Oe and 5.2 MHz in the layered films with a Cu film widths of 1 and 1.3 mm respectively. In addition, all the layered films exhibit a large negative GMI ratio at a relatively large field and it is associated with the easy axis orientation of the layered films. The increase of the positive maximum GMI ratio with an increase of Cu film width at 5.2 MHz may be due not only to the effect by the increase of Cu film width, but also to the difference in the easy axis orientations of the layered FeSiB/Cu/FeSiB films.

Frequency and Field Dependences of Giant Magneto-ImpedanceEffect in Sandwiched FeCuCrVSiB Films

The giant magneto-impedance (GMI) effect has been investigated in sandwichedFeCuCrVSiB films annealed at 300°C for 1.5 h. The frequency andfield dependences of the GMI have been observed in the frequency rangefrom 50 kHz to 13 MHz. The GMI ratio increases at first withincreasing frequency, and reaches its maximum value of 136% at a verylow characteristic frequency of about 4 MHz, and then decreases withfurther increasing frequency. These superior properties are related tothe special structure of the sandwiched films.

COMPUTATION ON GIANT MAGNETO-IMPEDANCE EFFECTS IN FERROMAGNETIC/NON-FERROMAGNETIC/FERROMAGNETIC LAYERED THIN FILMS

Based on the electromagnetic model of ferromagnetic/non-ferromagnetic/ferromagnetic layered films proposed in references [17] and [18] the enhanced giant magneto-impedance (GMI) effects and the GMI ratio dependence on the thickness of the constituent thin films are analyzed numerically in detail.It is showsn that larger difference of resistivity between the ferromagnetic and non-ferromagnetic layers as well as an optimum thickness of the layered thin films are beneficial to the improvement of the GMI effects.

The giant-magneto-impedance effect in FM/Ag/FM (FM≡FeCuCrVSiB) sandwich films

Sandwich films with the structure FM/Ag/FM have been prepared byradio-frequency sputtering and then annealed at an optimizedtemperature (here FM represents the FeCuCrVSiB amorphoussoft magnetic layer). The giant-magneto-impedance (GMI) effects forthe samples have been studied as a function of alternating-currentfrequency (50 kHz to 13 MHz) and external magnetic field. When thefrequency increases above a critical frequency f* (about150 kHz), the GMI ratio increases quickly with increasing frequency,and reaches a maximum value at a characteristic frequency fm ofabout 4 MHz. GMI ratios at fm as large as 109% and 135% wereobtained for longitudinal and transverse applied magnetic fields,respectively. These results are much better than those obtained forsingle-layer films, and the frequencies used in producing the effectare very low.

Giant Magneto-Impedance Effect in Sandwiched FeSiB/Cu/FeSiB Films

Giant magneto-impedance (GMI) effect has been realized in the sandwiched FeSiB/Cu/FeSiB films. With magnetic field Ha and ac current applied along the longitudinal direction of the sample, the GMI ratio increases with the increasing Ha, reaching a positive maximum value, and then decreases to negative values with further increase of magnetic field. Field dependence of the GMI ratio also indicates that the magnetic field corresponding to the maximum GMI ratio is different for various frequencies. The positive maximum GMI ratio is 17.2% for Ha=1600 A/m and frequency of 3 MHz. In addition, the films display a large negative GMI ratio with a magnetic field applied along the transverse direction and the value of the GMI ratio is about -13.4% for Ha=5600 A/m and frequency of 3 MHz.

Magnetic Properties and Giant Magneto-Impedance in Nanocrystalline FeCuCrVSiB Films

The giant magneto-impedance (GMI) effect has been observed in nanocrystalline FeCuCrVSiB films prepared by rf sputtering followed by an annealing treatment. The magnetic properties and the longitudinal and transverse GMI have been studied in detail. Field dependence and frequency spectra of GMI effect have been studied in the frequency range from 100 kHz to 13 MHz. Maximum GMI ratios as large as 50% and 25% were obtained at 13 MHz in the longitudinal and transverse cases, respectively. The field sensitivity of the longitudinal GMI is about 0.11% m/A at 13 MHz. The dependence of effective permeability on the frequency and magnetic field has been investigated.

The variation of giant magneto-impedance ratio in amorphous Co 66Fe 4NiB 14Si 15 ribbon annealed by pulsed Nd : YAG laser

We investigated the variation of giant magneto-impedance ratio and effective anisotropy field in Co 66Fe 4NiB 14Si 15 amorphous ribbon annealed by pulsed Nd : YAG laser at various annealing energies between 65–230 mJ/pulse in air. The pulsed Nd : YAG laser was pumped with Kr-lamp and consisted of an Nd : YAG rod of ∅ 5 mm×70 mm (AR-coated plane/plane), a full mirror and output coupler (30% transmission). The lasing wavelength is 1.064 μm and the pulsewidth is 220 μs. The GMI ratio shows thelargest value at 136 mJ/pulse (peak power is ∼620 W). While the GMI ratio is decreased for the further increment of annealing energy, the decreasing GMI ratio for the further increment of annealing energy is associated with the microstructural change by laser annealing.

Giant magnetoimpedance and domain structure in FeCuNbSiB films and sandwiched films

Longitudinal and transverse giant magnetoimpedance (GMI) effects are studied in FeCuNbSiB and FeCuNbSiB/Cu/FeCuNbSiB films. In regard to as-deposited single layer films, hardly any GMI effect can be detected, while for as-deposited sandwiched films, the maximum GMI ratios of 32% and 11% are obtained in longitudinal and transverse fields, respectively. After annealing, the maximum GMI ratios of 18% and 14% are obtained for the single-layer films in longitudinal and transverse cases, while for the sandwiched films, the maximum GMI ratios are 67% and 80% in longitudinal and transverse cases, respectively. A giant magnetoinductance ratio as large as 1733% is obtained in annealed sandwiched films at a low frequency of 100 kHz. In order to know the relation between GMI effect and magnetic properties of the samples, the domain structures are observed by the Kerr effect.