As-cast Ribbons Research Articles

High-frequency giant magnetoimpedance measurement and complex permeability behavior of soft magnetic co-based ribbons

We present a method for extracting the magnetic parameters of a soft magnetic Co-based alloy (Co/sub 68.25/Fe/sub 4.5/Si/sub 12.25/B/sub 15/) in the high-frequency regime (100 MHz-2.5 GHz). The method uses the magnetic sample (as-cast ribbon) as the conductor of a terminated microstrip transmission line. It uses the complex propagation constant of the line, obtained from open/short circuit input impedance measurements, to extract the per-unit-length series impedance. It then uses a theoretical model, based on the distributed parameters and the skin effect, to extract the bulk transverse relative permeability. The model considers the geometrical configuration of the magnetic conductor (ribbon) when determining the series impedance as well as the complex transverse relative permeability (/spl mu//sub tr/=/spl mu/'/sub tr/-j /spl mu/''/sub tr/). We report on the effect of applying and varying an external dc magnetic field.

MAGNETIC PROPERTIES OF AMORPHOUS Fe40Ni38B18Mo4 RIBBONS CONTAINING NANOCRYSTALLITES

Cut Fe 40 Ni 38 B 18 Mo 4 ribbons were annealed for two hours at various temperatures Ta between 400 and 540°C. All the ribbons were subjected to XRD, VSM (vibrating sample magnetometer) and ME (Mossbauer effect spectroscopy) investigations. A differential thermal analysis scan of an as-cast ribbon showed the presence of two exothermic peaks, the first beginning at 419.9°C and peaking at 429.7°C and the second beginning at 497.3°C and ending at 546.2°C. The XRD patterns of the ribbons showed the formation of FeNi 3 nanocrystallites in the lower T'a ribbons and (Fe, Ni, Mo) 23 B 6 crystallites in the ribbons annealed above 470°C. Different behaviors of the saturation magnetization were seen in the ribbons annealed between 400 and 450°C, between 450 and 490°C, and between 490 and 540°C. The ME spectra of the ribbons annealed in the three different temperature ranges also pointed to the presence of three crystalline Fe-compounds in these ranges. The XRD patterns and the coercivities (Hc) of the lower Ta ribbons point to the formation of nanocrystallites in these ribbons.

Correlations between low-field microwave absorption and magnetoimpedance in Co-based amorphous ribbons

Microwave power absorption measurements at 9.4 GHz were carried out on as-cast amorphous ribbons of nominal composition Co66Fe4B12Si13Nb4Cu. Two absorptions were observed: a small signal at a low dc field (<0.01T) and another one at a high dc field (∼0.1682T). The high-field signal shows all the features corresponding to ferromagnetic resonance. The low-field absorption (LFA) signal exhibits different characteristics such as hysteresis and a minimum in power absorption at zero magnetic field. A correlation between this LFA signal and magnetoimpedance measurements showed that both electromagnetic processes are associated with the same phenomenon.

Magnetic studies of melt spun NdFeAl–C alloys

Alloys with compositions Nd 60− x C x Fe 30Al 10 ( x=0, 1, 5 and 10) were processed by melt spinning at a tangential speed of 5 m/s. The as-cast ribbons were characterized by X-ray diffraction, Mössbauer Effect spectroscopy and their room temperature hysteresis loops. The substitution of Nd by C is found to affect the phase selection, from mainly DHCP-Nd for x=0 to DHCP-Nd /FCC-Nd for the other ones. Mössbauer spectra of all the as-cast samples indicate that Fe is present in crystalline magnetic phases as well as in a paramagnetic one. The major crystalline phase was identified as a μ-type (or A1) metastable phase, which is reported to have a large anisotropy field and a relatively high saturation polarization. Interstitial C stabilizes the μ-type phase and improves its average hyperfine field. The magnetic measurements display an increase of coercivity and remanence with the C concentration.

Nanocrystallization in amorphous Fe 40Ni 40(Si+B) 19Mo 1–2 ribbons

Cut Fe 40Ni 40(Si+B) 19Mo 1–2 ribbons were annealed for 2 h at various temperatures between 350°C and 600°C. XRD and Mossbauer effect spectroscopy (ME) measurements were then performed on all of the ribbons. The magnetic properties of several ribbons were measured using a vibrating sample magnetometer (VSM). A differential thermal analysis scan (over the range 20–800°C) of the as-cast ribbon showed two phase transitions; the first at 454°C and the second at 525°C. Both the XRD and ME spectra of the as cast, the 350°C and 400°C annealed ribbons showed that they were amorphous. The ME spectra of the 450°C, 475°C and 500°C annealed ribbons showed that these ribbons contained α-Fe, α-Fe(Si) and t-Fe 2B nanocrystallites. For the ribbons annealed above 550°C, crystallites of t-Fe 2B, t-Fe 3B, t-Fe 5SiB 2 and FCC-FeNi appeared, with the α-Fe and α-Fe(Si) crystallites disappearing. The sextets of all of the Fe compounds appeared in the ME spectra of the 525°C annealed ribbon. The VSM measurements supported the picture of a two-stage phase transitions; amorphous phase→a nanocrystalline phase (Fe-containing nanocrystallites in an amorphous matrix) at 454°C and then a second transition, the nanocrystalline phase→a disordered alloy containing Fe–B and Fe–Ni crystallites at 525°C.

Mechanical properties of amorphous Fe-based melt spun ribbons with Cr additions

The effect of Cr substitution for Fe on the mechanical properties of Fe 78− x Cr x Si 10B 12 and Fe 77.5− x Cr x Si 7.5B 15 (0⩽ x⩽8) melt spun alloy series is presented. The tensile strength of the as-cast ribbons increased slightly with the substitution of Fe by Cr from 1.5 GPa ( x=0) to 2.5 GPa ( x=8) for Fe 78− x Cr x Si 10B 12 alloys, and from 2.2 GPa ( x=0) to 2.9 GPa ( x=8) for Fe 77.5− x Cr x Si 7.5B 15 alloys. The Vickers microhardness remained almost constant for all Cr contents. In addition, the effect of annealing (30 min at various temperatures) on both, the tensile stress and microhardness of Fe 70Cr 8Si 10B 12 alloy was also determined. A gradual decrease with increasing annealing temperature was observed at the former and an increasing trend with higher anneal temperatures for the latter. Results are explained in terms of enhanced bond interaction metal–metalloid and of structural relaxation after heat treatment.

Air-flux magnetoelastic sensor based on inverse Wiedemann effect of amorphous ribbon

Abstract The inverse Wiedemann effect (IWE) of amorphous ribbon exhibiting positive magnetostriction constant has been studied. The effect of externally applied torsional stresses on IWE of as-cast Fe-rich ribbon of (Fe 0.79 Co 0.21 ) 81 Si 6.6 B 12.4 nominal composition has been investigated with the aim of using this material for technical applications. The observed high sensitivity of IWE on torsional stresses permits design of a new sensing element that allows to detect and measure small changes of an external air-flux flowing through the case of the sensing device. The magnetoelastic sensor as well as the necessary electronic circuitry have been successfully designed and tested.

High-Temperature Magnetic and Magnetotransport Properties of Melt-Spun Au80Fe20 and Au70Fe30

The high-temperature magnetic and magnetotransport properties of melt-spun Au100—xFex alloys (x = 20 and 30 at%) have been studied. As-cast Au80Fe20 ribbons are paramagnetic at room temperature, and exhibit a cluster-glass phase below 290 K. As-cast Au70Fe30 ribbons display similar features, with a higher paramagnetic temperature TC (415 K), which is reduced by low-temperature annealing. Both alloys exhibit an isotropic magneto-resistance (GMR) at room temperature; in Au80Fe20, the GMR arises from spin-dependent scattering of conduction electrons by atomic-size clusters of correlated, adjacent Fe spins. In Au70Fe30, the GMR is related to the effect of the external magnetic field, acting to destroy the locally canted arrangement of magnetic spins in the ordered phase.

Preparation and characterization of Fe–Nb–Cu–Si–B-based nanocrystalline soft magnetic materials

The nanocrystalline state of Fe 73.5Nb 3Cu 1Si 13.5B 9 ribbons exhibit superior soft magnetic properties with low coercivity, high permeability and moderate saturation induction value. However, due to the metastable nature of the materials, their properties depend very much on the preparation condition and heat treatment schedule. In the present work, the properties of the as-cast ribbons prepared at different nozzle diameter and separation between the quenching wheel and the nozzle were evaluated. The optimum conditions for getting continuous long ribbon from 150 g of ingot were established. The influence of heat treatment to get nanostructure and superior soft magnetic properties for selected ribbons were also studied. The ribbon surface quality was improved by reducing air pockets at the ribbon surface which was in contact with the quenching wheel.

Magnetic domains and magnetoimpedance effect during the nanocrystallization of Fe 73.5Cu 1Nb 3Si 16.5B 6 ribbons

Nanocrystalline Fe-based alloys have softer magnetic properties such as larger saturation inductions and permeabilities, smaller magnetostrictions, coercive fields and anisotropies compared to the same alloys in the amorphous state, which are suitable properties for using these materials as magnetic devices or sensors based on magnetoimpedance (MI) effect. Melt-spun ribbons made of Fe 73.5Cu 1Nb 3Si 16.5B 6 were annealed at different temperatures until crystallization, leading to devitrification of the initial state into a two-phase system (amorphous + FeSi grains), to study the correlations between the evolution of the domain widths, in both surfaces of the annealed samples, as well as other parameters such as saturation magnetostriction and electrical resistivity, with the MI effect response. Magnetic domains have been observed by means of the Bitter technique and we have established that after heat treatments, the domain width diminishes from 4.5±0.1 μm for the as-cast ribbon to 2.7±0.1 μm for the sample annealed at 475°C, which is in agreement with theoretical predictions. We also show that the maximum MI ratio is obtained for the ribbons annealed in the temperature range of 550–580°C, when the samples show an optimum nanocrystalline state and exhibit softer magnetic properties.

High coercivity Zr and Co substituted (Nd-Pr)-Fe-B nanophase hard magnetic alloys

The effects of Zr and Co substitutions for Fe on the magnetic properties of nanocrystalline near-stoichiometric (Nd/sub 0.75/Pr/sub 0.25/)/sub 12/(Fe/sub 1-x/Co/sub x/)/sub 82-z/Zr/sub z/B/sub 6/ (x=0,0.1,0.2 and z=0-4) alloy ribbons are reported. The nanoscale structures were derived by devitrification annealing of amorphous as-cast ribbon. Very good combinations of energy product, (BH)/sub max/ (/spl sim/160 kJ/m/sup 3/) and intrinsic coercivities, /sub i/H/sub c/ (within the range 800-1400 kA/m for various Zr concentrations) were achieved for the Co-free alloys although the Zr addition resulted in some reduction in T/sub c/. For alloys in which, also, 10 and 20% of the Fe was substituted by Co, excellent remanence enhancement, J/sub r/ (to >1 T) were achieved with 1 at% Zr addition. Combined with excellent squareness of the J-H second quadrant, this gave (BH)/sub max/ up to 175 kJ/m/sup 3/, together with Curie temperatures, T/sub c/ of >375/spl deg/C and >460/spl deg/C for 10 and 20% Co, respectively, and with only minor reductions in /sub i/H/sub c/. The role of Zr in promoting uniform and refined grain structures and enhancing the magnetic properties will be discussed.

Low-temperature hardening of coercivity of amorphous alloys

The temperature dependence of the coercivity was measured in Fe 85− x Co x B 15 and Co 77B 23 as-cast amorphous ribbons. A fast increase of the coercivity was found for T<100 K. The temperature dependence of the susceptibility, pinning field, saturation magnetostriction and saturation magnetisation was used to describe the temperature dependence of the coercivity. The hardening of the coercivity for low temperatures ( T<100 K) is well described by short-range pinning mechanism, whereas for high temperatures, magnetostrictive interactions between internal stresses and the domain walls lead to a pinning effect.

Effect of roll speed on the magnetic properties of nanocomposite PrFeB magnets prepared by melt-spinning

Rapid solidified Pr x Fe 94− x B 6 alloys, with x ranging from 6 to 10 at%, were prepared by melt-spinning at several roll speeds to obtain nanocomposite PrFeB magnets with enhanced properties. Magnetic properties and grain-size measurements were performed on as-cast ribbons and were correlated to roll speed. It was found that the greatest J r enhancement occurred at roll speeds that led to grain sizes below ∼30 nm. Deviations from this optimum value, caused either by partial amorphisation or grain coarsening, greatly affected the values of J r, jH c and ( BH) max.

Fluence effects on the magnetic properties of Fe81B13.5Si3.5C2 metallic glass produced by pulsed laser deposition

A metallic glass target of Fe81B13.5Si3.5C2 ribbon was ablated under pulsed focused laser irradiation at a high fluence, Φ=3, 5, 6, 7.5, and 10 J/cm2. X-ray diffraction was performed on the resulting films, demonstrating the amorphous nature of the samples. Hysteresis loop measurements were recorded at 4.2 K in an applied magnetic field of 1.5 T to show differences in the saturation magnetic moment and coercivity between the as-cast ribbon and laser-ablated films. Conversion electron Mössbauer spectra were used to obtain the fluence dependence of the hyperfine magnetic field and magnetic texture parameter. At low laser fluences, the magnetic moments were predominantly oriented in the plane of the film. For intermediate values of the laser fluence, a random distribution of magnetic-moment directions was achieved. For high laser fluences, however, an out-of-plane orientation of the magnetic moments resulted. The films have prospective applications in magnetic sensors, switches, and concentrators.

Structural configuration and magnetic properties of the rapidly solidified CuCo alloy

The internal friction as a function of temperature and the giant magnetoresistance for varying magnetic field have been measured on Cu 90Co 10 ribbons obtained by planar flow casting with different quenching rate. The results are discussed considering the presence of quenched-in Co precipitates in the Cu matrix of the as-cast ribbons and different levels of dispersion of Co in the Cu matrix in the two cases.

MFM of nanocrystalline NdFeB: a study of the effect of processing route on the micromagnetic structure

The magnetic domain structure of near stoichiometric (Nd 11.8Fe 82.3B 5.9) nanocrystalline alloy ribbon has been examined using magnetic force microscopy (MFM) as a function of processing conditions. Amorphous structured ribbons of Nd 2Fe 14B with an average thickness of 25 μm were produced by chill block melt-spinning. Subsequently, samples were heat treated at 600°C for 4 min to produce a nanocrystalline structure consisting of Nd 2Fe 14B grains of average size ∼35 nm. These were compared to ribbons of the same composition, but melt spun directly to the nanocrystalline state, also with an average grain size of ∼35 nm. MFM imaging was undertaken using CoCr, NiFe and Fe/SiO 2 coated pyramidal Si tips. The as-cast amorphous ribbons exhibited weak magnetic contrast with a correlation length of 130±20 nm, but with a small elongation in one direction, as shown by Fourier transforms of the MFM images. Nanocrystalline samples produced by devitrification exhibited longer correlation lengths of 1000±50 nm and with a stronger angular component to the Fourier transform. The application of a 5 T field to the nanophase sample in a direction normal to the sample plane resulted in a reduction of the correlation length to 600±50 nm and a reduction in the directionality of the magnetic contrast. However, the application of a 5 T field in the plane of the ribbon resulted in an elongation of the contrast in a direction parallel to the applied field, irrespective of the in-plane field direction. In contrast, ribbon melt spun directly to a nanocrystalline structure exhibited a uniform Fourier transform both in the as-cast and remanent states. The length scale of dominant magnetic structure was 350±30 nm for the as-cast and 620±30 nm for the remanent state. Within the dominant magnetic structure, a finer structure was apparent, of a scale comparable to the grain size.

Modelling of the stress distribution in amorphous toroidal transducer cores

It is very important to understand, stress distribution and variation of stress due to applied displacement in toroidal cores in order to improve the sensitivity, accuracy and repeatability of the amorphous toroidal transducers. For this purpose a commercially available mechanical FEM package called PAFEC®, has been used to model stress distributions around the circumference of toroidal transducer cores, and the variation of the stress on the inner, middle and the outer surfaces of the Fe based as-cast amorphous ribbon toroidal transducer core were studied.

Study of frequency dependencies of the complex magnetic ac-permeability aftereffect in amorphous Fe64Co21B15 and Fe8Co77B15 alloys

The frequency dependencies of the complex magnetic permeability and its aftereffect phenomenon in as-cast and annealed Fe64Co21B15 and in as-cast Fe8Co77B15 amorphous ribbons were studied. The measurements of these properties were carried out at frequencies between 1 and 120 kHz. The behavior of the frequency dependence of real and imaginary parts of the ac permeability and aftereffect were analyzed using the magnetic domain wall motion model. A change of the restoring force coefficient and the damping parameter with time was considered for the study of frequency dependency of the magnetic relaxation.

Structural relaxation and associated ΛH effect in the Fe‒Cu‒Nb‒Si‒B system

Abstract The microstructural evolution from the amorphous to nanocrystalline phase in the Fe73·5Cu1Nb3Si13·5B9 alloy produced by planar flow casting was studied by performing Young's modulus, internal friction and initial susceptibility measurements against temperature on as-cast ribbons and on samples submitted to selected furnace heating treatments. Moreover, the room-temperature magnetoelastic behaviour in the as-prepared ribbons and in samples annealed in the 570–850 K range was investigated through the analysis of the ΛE effect. The results indicate that a structural relaxation process of the amorphous phase occurs starting from 450-500 K. In particular, a strong magnetoelastic response observed in samples annealed in the 710–745 K range, namely at temperatures very close to the nanocrystallization temperature (760–770 K), suggests an increase in the saturation magnetostriction with respect to the as-cast alloy, connected with atomic rearrangements causing a compositional fluctuation in the amorphous...

The effect of quenching rate on the nanocrystallization of amorphous FeCuNbSiB

Amorphous ribbons with composition Fe 73.5Cu 1Nb 3Si 13.5B 9 were produced by planar flow casting using different values of the wheel velocity, within the range 20–32 m/s. In order to understand the effect of the quenching rate on the subsequent degree of nanocrystallization, a detailed characterisation of as-cast and annealed ribbons at 500 and 540°C has been performed using Mossbauer spectroscopy and X-ray diffraction.