Soft Magnetic Ribbons Research Articles

Field-Concentrator-Based Resonant Magnetic Sensor With Integrated Planar Coils

This paper reports on a highly sensitive resonant magnetic microsensor with a shift of the mechanical resonance frequency f res depending quadratically on the magnetic flux density B to be measured. The sensor combines an electrostatically driven micromechanical resonator with a geometrically optimized planar magnetic concentrator with two narrow gaps. Sensitivities df res/dB of several megahertz per tesla are achieved without complex feedback and modulation electronics. When the device is operated in a switched auxiliary magnetic field using two integrated planar coils, the raw parabolic response of the sensor is translated into a resonance frequency difference proportional to B . For a coil current of plusmn120 mA, the device offers a sensitivity of 1.91 MHz/T and a resolution of 1.3 muT . In vacuum, a resolution of 400 nT is demonstrated. With these performance numbers, applications such as a microelectromechanical (MEM) compass for the measurement of the Earth's magnetic field can be envisaged. The fabrication process of the microsensor combines the following: 1) the micromachining of a silicon-on-insulator substrate for the MEM structure; 2) the attachment and structuring of a thin amorphous soft magnetic ribbon for the magnetic concentrator; and 3) the UV-laser ablation for the micropatterning of the concentrator gaps. Thermal effects due to high coil currents were analyzed in detail, as they play an important role in the reported microsensor design.

Magnetoelectric effects in piezoelectric/soft magnetic amorphous FeCo-based ribbon composites

Magnetoelectric effect has been investigated in several multiferroic laminates generated by inserting a lead-zirconate titanate PZT plate between sheets of highly soft magnetic amorphous FeCo-based alloy ribbon. The results show that the magnetoelectric coefficient αE (= dE/dH) depends on the rest glass-forming elements as well as the concentration of Co substitution. Giant magnetoelectric is found for the composite of Fe73.5Cu1Nb3B9Si13.5 ribbon, where αE as high as 1000 mV/cmOe at low field of 50 Oe. aE can be further improved up to 1170 mV/cmOe at 20% Fe substituted by Co. The higher the Co concentration, the lower magnetoelectric effect is observed. High magnetoelectricty at low field makes these composites suitable for special applications such as smart sensors for detecting microtesla magnetic fields and especially biosensor for magnetic label detection.

Influence of the demagnetizing field on the determination of the magnetocaloric effect from magnetization curves

The influence of the demagnetizing factor (N) on the magnetic entropy change (ΔSM) curves is studied for materials with a second order phase transition. For this purpose, a soft magnetic amorphous ribbon is measured for different orientations of the magnetic field with respect to the plane of the sample. For temperatures below the Curie temperature (TC), the increase in N causes a decrease in ΔSM, while for temperatures above TC no change in the shape of the curves has been found for the different orientations, as expected. In order to eliminate this influence of N and compare the ΔSM(T) curves for samples with different shapes, the recently proposed universal curve for the magnetocaloric effect can be used.

Microwave power absorption analysis in the devitrification process of Co-based amorphous ribbons

Melt-spun Co 66 Fe 4 B 12 Si 13 Nb 4 Cu soft magnetic ribbons were devitrified at low annealing temperatures (623 K), for times 5–20 min. Microwave power absorption measurements at 9.4 GHz (X-band) were carried out in two geometries. In geometry 1, the ribbon’s plane was oriented parallel to AC magnetic field. For the orientation 2, the ribbon’s plane was normal to the AC magnetic field. In both cases, the ribbon’s axis was parallel to the DC magnetic field. For both orientations, two absorptions were observed: the first corresponds to a low field microwave absorption (LFA) centered in zero dc magnetic field, and a higher field absorption corresponding to the ferromagnetic resonance (FMR). In the geometry 1, a single FMR spectrum was observed for all the samples, with a shift in resonant field as annealing increased. For geometry 2, evidence of the superposition of two FMR signals was observed. FMR spectra are therefore due to a combination of two different magnetic phases corresponding to the amorphous matrix and nanocrystallites. Deconvolution calculations were carried out on FMR spectra to separate the contributions. Their behavior as a function of annealing time was in good agreement with the magnetic softening, also obtained with LFA results. The differences in microwave absorption, for both geometries, can be explained by differences in the electromagnetic wave propagation volume.

Effects of Surface Abrasion on Magnetization of VITROVAC 6025Z Ribbons

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The effects of abrading with sandpaper the surface of VITROVAC 6025Z ribbons on the parameters of their <formula formulatype="inline"><tex Notation="TeX">$M$</tex> </formula>-<formula formulatype="inline"><tex Notation="TeX">$H$</tex></formula> loops (the coercive field <formula formulatype="inline"><tex Notation="TeX">$H_{c}$</tex> </formula>, the position of the center <formula formulatype="inline"><tex Notation="TeX">$C$</tex></formula>, etc.) have been investigated. The application of surface fields <formula formulatype="inline"><tex Notation="TeX">$H_{P}$</tex> </formula> (generated by core currents) enabled us to single out the effects of surface domains (surface domain structure (SDS) pinning) and surface irregularities (intrinsic pinning) on domain wall (DW) pinning in abraded and unabraded ribbons. The abrasion enhances the intrinsic DW pinning (increases <formula formulatype="inline"> <tex Notation="TeX">$H_{c}$</tex></formula>) and strongly modifies the SDS pinning which shows up in specific variations of <formula formulatype="inline"> <tex Notation="TeX">$H_{c}$</tex></formula> and <formula formulatype="inline"> <tex Notation="TeX">$C$</tex></formula> with <formula formulatype="inline"> <tex Notation="TeX">$H_{P}$</tex></formula>. In particular, the effect of <formula formulatype="inline"><tex Notation="TeX">$H_{P}$</tex></formula> on surface domain structure (SDS) pinning, which was symmetrical in unabraded ribbon becomes asymmetrical upon abrasion (i.e., different on opposite surfaces). A simple model for the influence of <formula formulatype="inline"><tex Notation="TeX">$H_{P}$</tex> </formula> on magnetization processes in soft magnetic ribbons describes the observed variations of <formula formulatype="inline"><tex Notation="TeX">$H_{c}$</tex> </formula> and <formula formulatype="inline"><tex Notation="TeX">$C$</tex> </formula> with <formula formulatype="inline"><tex Notation="TeX">$H_{P}$</tex> </formula> in both abraded and unabraded ribbons</para>

Nanocrystalline soft magnetic ribbon with α″-Fe 16N 2 nanocrystallites embedded in amorphous matrix

A nanostructure with α″-Fe 16N 2 nanocrystallites embedded in an amorphous matrix was prepared by annealing Fe 92B 8 amorphous alloy in a NH 3+H 2 gas mixture stream with subsequent quenching and annealing. The average grain size and the volume fraction of the α″-Fe 16N 2 phase are found to be 18 nm and 54%, respectively. The prepared sample exhibits a saturation magnetization of 2.35 T, a coercive force of 11.4 A/m, an initial permeability of 9.1×10 4 and a relaxation frequency of 4.1×10 4 Hz.

Influence of Ge on magnetic and structural properties of Joule-heated Co-based ribbons: Giant magnetoimpedance response

Studies of magnetic and structural properties of Fe 3.5Co 66.5Si 12− x Ge x B 18 ( x=0, 3, and 6) soft magnetic ribbons obtained by melt-spinning were performed. The samples were submitted to Joule-heating treatments with different maximum current values (0.01, 0.05, 0.1, 0.2, and 0.8 A, respectively) with steps of 0.01 A and times by step of 1, 2, and 10 s). X-ray diffraction, temperature dependence of magnetization (for the as-quenched samples), coercivity and giant magnetoimpedance (GMI), measured at different frequencies (100, 500, and 900 kHz, respectively) were performed. All the samples crystallized at annealing currents higher than 0.4 A, which was consistent with the magnetic hardening of the material. Coercivities less than 1 A/m were obtained for the three samples between 0.1 and 0.2 A. Maximum value of GMI response was observed for the sample without Ge in the as-quenched state.

Characterisation of rapidly solidified nanocrystalline soft magnetic ribbons based on FeSiB with P and Ga additions

AbstractSoft magnetic materials derived from rapidly solidified FeSiB alloys exhibit excellent soft magnetic properties due to the crystallisation of nanoscale α‐iron grains in an amorphous matrix. It has been proposed that decreasing the critical solidification rate by choosing the multi‐atomic alloying system with negative enthalpies of mixing among elements can lead to further grain refinement. In the present work, an alloy with P, Ga and Al additions to satisfy the rule for decreasing the critical solidification rate was produced. The structures of as‐cast and annealed alloys were investigated in detail using FESEM, supplemented by EDS, WDS and EBSD analytical tools. Additionally, surface analysis by AES and XPS was performed to characterise the phases. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Failure Behaviour of Fe- and Co-Based Amorphous Soft Magnetic Ribbons

Failure Behaviour of Fe- and Co-Based Amorphous Soft Magnetic Ribbons

Structural Changes in New Rapidly-Quenched Finemet Type and Hitperm Type Alloys

Structural transformations taking place during annealing of rapidly-quenched soft magnetic ribbons from the Finemet type and Hitperm type alloys were investigated. The X-ray quantitative phase analysis and X-ray diffusion scattering methods were used. It was found that the structural changes in the alloys studied, including crystallisation process and short-range ordering in the amorphous phase, are reflected by the changes in their magnetic properties. These properties, and particularly the magnitude of saturation induction Bs , depend on the content of cobalt and silicon in these alloys and on short-range order in the amorphous phase.

Wide-angle magnetoimpedance field sensor based on two crossed amorphous ribbons

Soft magnetic amorphous ribbons have been exhaustively studied in order to use them as magnetic field sensitive elements based on the magnetoimpedance effect, MI. In comparison with other materials they exhibit some disadvantages like double-peak response for small values of the applied magnetic field due to the peculiarities of the surface anisotropy. In this work, magnetic properties, MI effect, and the angular dependence of the impedance on the applied magnetic field direction have been studied for CoFeMoSiB amorphous ribbon based sensitive elements in two configurations. The first one is a classic MI prototype with one amorphous ribbon sensitive element installed on a printed circuit board. In the second configuration two amorphous ribbons with the same size are placed in the board forming an angle of 15° between them. MI effect is measured in a frequency range from 0.4 to 10 MHz for exciting current amplitudes ranging from 2 to 20 mA. For this prototype of sensor device formed by two crossed amorphous ribbons, it is possible to obtain single-peak MI response and independent on the orientation of the external field output signal in a wide range of the angles from 0 to 45°, in contrast with the double peak and angle dependent response obtained for single ribbon sensitive element.

High permeability nano-crystalline FeSiBTaAg ribbons obtained by direct casting

Nano-crystalline soft magnetic ribbons, being extensively used as magnetic cores for switching power supplies, have been invariantly obtained by melt-spinning followed by post-annealing. Reported herewith are the attainment, by direct-casting without annealing, of nano-crystalline Fe 77.4− x Si 15.5B 7Ta x Ag 0.1 ( x = 1, 2) ribbons with superior soft magnetic properties (named TAGMET after the addition of Ta and Ag). The grain size of nano-crystalline α-FeSi, from 20 to 30 nm, varies with composition and quenching speeds. As-spun Fe 75.4Si 15.5B 7Ta 2Ag 0.1 ribbons consisting of ∼25 nm nano-crystals exhibit a saturation magnetization of 157 emu/g (1.45 T), an effective permeability of 56,000 at 1 kHz, and coercivity, 8 A/m. With the combination of easier manufacturing process and excellent soft magnetic properties, this alloy is competitive in industrial applications versus the well-known FINEMET.

Nanocrystalline soft magnetic ribbons with high relative strain at fracture

Melt-spun nanocrystalline/amorphous composite ribbons (e.g., Finemet and Nanoperm) have excellent soft magnetic properties but are notoriously brittle after crystallization. In this letter, the authors present their findings of increased relative strain at fracture in Co-rich nanocomposite soft magnetic ribbons compared to conventional nanocomposite ribbons. Bending tests of the Co-rich ribbons show relative strain at fracture values more than twice as high as a Nanoperm ribbon. These Co-rich alloys have excellent soft magnetic properties with potential for high temperature applications. A (Co0.90Fe0.08Ni0.02)88Zr7B4Cu1 ribbon annealed at 823K for 3600s has a high saturation magnetization of 131Am2∕kg and a low coercivity of 8A∕m.

Ultra-small-angle scattering with polarized neutrons

Ultra-small-angle neutron scattering (USANS) has been established as an effective technique for the study of structures in the micrometre range in recent years. Consequentially this method has been extended to magnetic structures of corresponding size. We present the instrument arrangement and first experimental results. The instrument itself is a double crystal diffractometer in Bonse–Hart configuration which takes advantage of the narrow angular width of the perfect crystal reflection to obtain an extremely high angular resolution of the scattering vector. The neutrons are loss-free polarized by permanent magnetic prisms located between the monochromator crystal and the sample. Neutrons with opposite polarization are separated to a large extent and their different scattering behaviour may be studied in a single measurement without additional manipulation of the neutron spin. In this manner we are able to separate the magnetic and nuclear contribution to the scattering. We present first exemplifying measurements on ferromagnetic rods and wires, and on soft-magnetic ribbons. Related experiments were performed at the USANS facility of the TRIGA reactor at the Vienna University of Technology and at the combined neutron interferometer/USANS instrument S18 at the ILL, Grenoble.

Effect of magnetic field–current annealing on the magnetoimpedance of Co-based ribbons

The roles of applied magnetic field during the current annealing of Co68.15Fe4.35Si12.5B15 soft magnetic amorphous ribbons have been studied. The Joule heating process causes a complex domain structure which is related to the circular field generated by the current. We have shown that magnetic field–current annealing modifies the transverse permeability and under suitable conditions, enhances the GMI response.

Novel Fabrication Process for the Integration of MEMS Devices with Thick Amorphous Soft Magnetic Field Concentrators

AbstractThis paper reports a novel fabrication process enabling the integration of mechanical MEMS devices with thick amorphous soft magnetic field concentrators. The integration process combines silicon on insulator technology for the MEMS device fabrication and epoxy-resin-based attachment of 18-µm-thick amorphous soft magnetic ribbons followed by a wet chemical structuring process. The fabrication process is reported on the basis of a field-concentrator-based resonant magnetic sensor combining an electrostatically driven micromechanical resonator and a planar magnetic field concentrator with two narrow gaps. For realization of the concentrator gaps, the integration process is extended by micro-patterning of the soft magnetic ribbons via UV-laser ablation using an excimer laser system. The characterization of the fabricated resonant magnetic sensor using a stroboscopic video microscope for in-plane motion measurement shows a high sensitivity of 390 kHz/T at a magnetic flux density of 158 µT.

The crystallization and properties of alloys with Fe partly substituted by Cr and Cu fully substituted by Au in Finemet

The structure, crystallization and magnetic properties of ribbons obtained by first making amorphous ribbons and then objecting them to a crystallization annealing have been published elsewhere by us previously. In the present work the soft magnetic ribbons Fe 73.5− x Cr x Si 13.5B 9Nb 3Au 1 (numbers indicate at.%, x = 1–5) are prepared by fast quenching on a single copper wheel. X-ray diffraction patterns show that the as-cast samples are amorphous. Differential scanning calorimetry analysis indicates that the crystallization temperature of the α-Fe(Si) phase is a little higher than that of pure Finemet. With the same annealing conditions, the crystallization volume fraction decreases with increasing Cr content substituted for Fe. Hysteresis loops of as-cast samples measured by Permagraph show that domain walls are pinned. After appropriate annealing, the ultrasoft magnetic properties of nanocomposite materials are established. The magnetic entropy change, |Δ S m|, of studied samples has been determined, and a giant magnetocaloric effect is found. Our materials could be considered as promising magnetic refrigerants working at high temperatures (several hundreds °C).

Deconvolution of ferromagnetic resonance in devitrification process of Co-based amorphous alloys

Ferromagnetic resonance (FMR) measurements were carried out on soft magnetic amorphous ribbons of composition Co 66Fe 4B 12Si 13Nb 4Cu prepared by melt spinning. In the as-cast sample, a simple FMR spectrum was apparent. For treatment times of 5–20 min a complex resonant absorption at lower fields was detected; deconvolution calculations were carried out on the FMR spectra and it was possible to separate two contributions. These results can be interpreted as the combination of two different magnetic phases, corresponding to the amorphous matrix and nanocrystallites. The parameters of resonant absorptions can be associated with the evolution of nanocrystallization during the annealing.

Thermal, magnetic, and structural properties of soft magnetic FeCrNbCuSiB alloy ribbons

The thermal, magnetic and structural properties of amorphous magnetic Fe 73.5− x Cr x Nb 3Cu 1Si 13.5B 9 alloy ribbons, with x = 0 , 2, 4, 6, 8, and 10, were studied by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), magneto-impedance measurements and X-ray diffraction (XRD). The ribbons exhibit ultrasoft magnetic behavior, especially giant magneto-impedance effect, GMI. A three-peak behavior was observed in GMI curves. Particular attention has been given to observation of crystallization kinetics via DSC and TGA. The primary crystallization T pcr, and Curie T c, temperatures were determined from DSC and TGA data, respectively. The effect of partial substitution of iron by Cr on the thermal and magnetic properties is discussed.

High saturation magnetization and soft magnetic properties of nanocrystalline (Fe,Co)90Zr7B3 alloys annealed under a rotating magnetic field

The effects of magnetic-field annealing on the soft magnetic properties of nanocrystalline (Fe1−xCox)90Zr7B3 (x=0, 0.1, 0.2, and 0.3) have been investigated. The annealing-induced uniaxial anisotropy (Ku) in these alloys was found to follow an x2 dependence and Ku appears to reflect the population density of Co–Co atomic pairs. The annealing-induced anisotropy is suppressed by applying a rotating field during annealing and the coercivity is reduced by up to 60%. Nanocrystalline (Fe0.8Co0.2)90Zr7B3 annealed under a rotating field of 640kA∕m exhibits a low coercivity of 9.1A∕m and high permeability values (under 0.4A∕m) of 4500 at 1 kHz and 3100 at 100 kHz along with a high saturation magnetization of 1.74 T. These permeability values are comparable to those of Fe-based amorphous alloys while the saturation magnetization is clearly higher than those of amorphous or nanocrystalline soft magnetic alloy ribbons developed to date.