M. Kuźmiński

Magnetostriction and its temperature dependence in FeCuNbSiB nanocrystalline alloy

Abstract The temperature dependencies of the linear saturation magnetostriction of Fe73.5CuNb3Si15.5B7 nanocrystalline alloy have been measured for the samples exhibiting a wide range of the crystalline phase volumetric fraction obtained by a proper annealing procedure. It has been proved that the effective magnetostriction of this material can be interpreted as a volumetrically weighted balance among two contributions, a negative one (for the bcc-Fe(Si) nanocrystallites) and a positive one (for the residual amorphous matrix). The measured temperature dependencies of the effective magnetostriction have been analyzed in order to calculate both contributions to this quantity. This analysis was performed assuming linear as well as quadratic approximation of the dependence of the effective magnetostriction on the nanocrystalline fraction showing that the former reflects better the properties of the material. The above analysis also showed that, in order to obtain zero-magnetostrictive material at room temperature, the fraction of nanocrystallites should be relatively large (∼ 70–80%).

The effect of particle size and surface-to-volume ratio distribution on giant magnetoresistance (GMR) in melt-spun Cu–Co alloys

Abstract Giant magnetoresistance (GMR), magnetization and structure of granular Cu 90 Co 10 alloy were investigated. The annealed sample is inhomogeneous with respect to the Co-particle sizes and interparticles distances and, therefore, not all particles behave superparamagnetically. The observed deviation from the expected theoretically quadratic dependence of GMR on magnetization can be attributed to differentiated surface-to-volume ratio of superparamagnetic particles as well as to the presence of a small amount of ferromagnetic phase which is created by relatively large Co-rich regions.

Evolution of transverse permeability with DC-field in Co-based metallic glass ribbons

A simple model is proposed that allows to calculate the penetration depth and the mean transverse permeability in magnetic elements of a rectangular cross-section they are used to study the giant magnetoimpedance effect. As an instance of the use of this model, both the mentioned quantities were calculated for the Co-based metallic glass ribbon. Their evolution with the applied axial DC-field at various frequencies of the AC-current, flowing along the ribbon, is presented. A comparison of the experimental data with those calculated by the model, shows that the latter gives only a qualitative approximation of the measured dependencies.

Tailoring soft and hard magnets by annealing Co-based metallic glass

Abstract Co 67 Fe 4 Mo 2 Si 17 B 11 metallic glass ribbon has been subjected to the isothermal annealing at temperatures in the range 250–600°C so as to produce a series of samples with gradually coarser microstructure. For this series of samples a giant increase of the coercivity, exceeding five orders of magnitude, is observed. It shows a possibility to tailor soft or hard magnets using the same parent material. An abrupt increase of the coercivity occurs in a relatively small range of annealing temperatures between 480 and 520°C, and is mainly due to a strengthening of the pinning effect of the precipitates (fine crystalline structure) on the domain walls. Samples annealed at higher temperatures become fully crystallized. First, the metastable phase(s) is created which decomposes to the stable phases at still higher temperature. Coercivity for fully crystallized samples shows first a narrow plateau and afterwards a gradual decrease of its value with increasing temperature of annealing. Magnetic and microstructural properties of the samples, annealed at various temperatures, were investigated applying a number of complementary techniques including DSC and TGM methods, X-ray diffraction, TEM, strain-modulated FMR spectroscopy as well as conventional magnetic measurements.

Magnetic properties and domain structure investigation of laser treated Finemet

We describe the influence of the density of dotted lines produced by laser scribing on the domain structure and shape of the hysteresis loops, which are different for samples with high density of dotted lines in comparison to that of samples with optimum density of dotted lines (leading to largest decrease of loss) was observed.

Induced transverse magnetic anisotropy and domain structure in Co-based amorphous ribbons

Abstract The influence of transverse magnetic field annealing on a domain structure, the value of the induced transverse magnetic anisotropy K u , coercivity and magnetic remanence of Co 71.5 Fe 2.5 Mn 2 Mo 1 Si 9 B 14 amorphous ribbons of different widths (6, 11, 15 mm) has been investigated. Near-full reorientation of the ribbon easy axis from the longitudinal to the transverse direction and the highest value of K u = 110 J/m 3 were obtained for the transverse magnetic field H T = 160 kA/m. On the other hand, only partial reorientation of the easy axis was developed for smaller values of H T . In the initial magnetizing field range, the magnetization process proceeds by reversible rotation of the magnetization vector for H T = 160 kA/m. Domain wall movements are predominant for H T = 8 and 40 kA/m.

Magnetic properties of surface layers of Fe71.5Si15.5-xCu1Nb3B9Alx(x = 0,1,2,3 at%) alloys with substitutions by aluminium

Abstract In this paper we describe the influence of the composition and the annealing treatment on the domain structure of Fe–Si–Cu–Nb–B–Al alloys with different Al/Si content. Our observations were compared with the bulk and surface layer coercivity. We have found that aluminium influences magnetic properties and the domain structure of these alloys. Since the crystallization temperature of these alloys decreases with increasing Al content, our samples did not show any improvement of soft magnetic properties as compared with Finemet.

Magnetostriction of Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloy

Abstract Systematic investigations of low effective saturation magnetostriction of FeCuNbSiB nanocrystalline alloys, performed on a series of samples with different volumetric fraction of the crystalline phase, have shown that this behavior results from the balance of two contributions with opposite sign originating from the crystalline and amorphous phases.

Magnetic hardening in gradually devitrified Co-based glassy alloys

It is shown that gradual devitrifiation of non-magnetostrictive Co-based metallic glass leads to a giant, five orders of magnitude, increase of its coercivity. This magnetic hardening is due to the pinning of domain walls by growing fine crystallites much smaller than the domain wall width, the number and size of which increase with an increase of the annealing temperature.

Induced transverse magnetic anisotropy in Co-based amorphous alloys with different values of the saturation induction

Abstract The magnetic properties and domain structure of three near-zero magnetostrictive amorphous alloys: Co 71.5 Fe 2.5 Mn 2 Mo 1 B 14 Si 9 , Co 76 Fe 2 Mn 4 B 12 Si 6 and Co 68 Fe 4 Mo 1.5 B 13 Si 13 (at%), with different values of the saturation induction, were investigated as functions of two-step magnetic annealing parameters: preannealing time t a and strength of transverse magnetic field H T applied during cooling.