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The cumulant method is a model-independent technique based on the expansion of extended X-ray absorption fine structure (EXAFS) amplitudes and phases as a series of cumulants of the interatomic distance distribution. Results show evidence of simple grain boundary formed as amorphous–crystal interface region around BCC Fe nanocrystals. This interface region initially growth along with the growth of the Fe nanocrystals. However, in the latter stage of nanocrystallization, additional contribution of statically disordered interface is formed in nanograin boundaries hindering the grain growth. The disordered interfacial regions can help to explain nanocrystallization phenomenon of Fe85Zr7B6Cu2 alloys.

Magnetically soft nanomaterials obtained by controlled crystallisation of metallic glasses are the newest group of materials for inductive components. In particular, research is carried out in the field of alloys for high temperature applications. This kind of materials must meet two basic requirements: good magnetic properties and stability of properties and structure. In the present work the magnetic properties and structure of Fe-Co-Hf-Zr-Cu-B (HITPERM-type) alloys were investigated, as well as their stability. Differential thermal analysis, (DTA), X-ray diffractometry (XRD), transmission electron microscopy (TEM), magnetometry (VSM) and quasistatic hysteresis loop recording were used to characterise structure and properties of the alloys investigated. Optimisation against properties and their stability was performed, resulting in formulation of chemical composition of the optimum alloy, as well as its heat treatment.

Amorphous and slightly crystallized CoNbCuSiB alloys were studied by the magnetisation measurements. Precipitation of Co-based crystallites destroys the ferromagnetic ordering of the amorphous alloy and leads to a cluster-glass state. At elevated temperatures, the grains embedded in the paramagnetic matrix exhibit the superparamagnetic behaviour.

Local structural changes are studied occurring during transformation from amorphous to nanocrystalline phases of Fe 85 Zr 7 B 6 Cu 2 , Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 and Fe 66 Cr 8 Cu 1 Nb 3 Si 13 B 9 alloys. The nanocrystalline state of a formerly amorphous alloy was achieved by heat treatment at temperatures between 420 and 600°C. The high-resolution transmission electron microscopic images have shown the average size of the Fe and Fe(Si) nanograins in nanocrystalline alloys ranging from 5 to 15 nm in alloys at different stages of crystallisation. X-Ray absorption spectra at the K-edge of Fe, Cu and Cr atoms for nanocrystalline alloys measured using synchrotron radiation have shown a different local structure, namely the structure bcc Fe around Fe atoms, fcc Cu around Cu atoms and amorphous around Cr atoms. The growth of fcc Cu clusters before the nucleation of bcc Fe grains in nanocrystalline alloys was observed. It can be considered as a basic mechanism responsible for nanocrystalline grain formation. The FEFF8 program was used for calculations of X-ray absorption spectra up to about 260 eV above the Fe K-edge for bcc Fe metal and Fe 3 Si compound in terms of self-consistent muffin-tin potential approximation and full multiple scattering approach. The theoretical spectra well explained the experimental result that the amplitude of EXAFS oscillations in Fe 3 Si was considerably decreased by the presence of Si atoms in comparison to that for Fe metal.

Properties of nanocrystalline magnets exhibiting low Curie temperature of the residual amorphous matrix, obtained by partial crystallization of Co–Nb–Cu–Si–B melt-spun ribbon, were studied by means of ferromagnetic resonance (FMR) as well as conventional magnetometry. The results acquired in FMR measurements, performed at the temperature ranging from 4.2 up to 300 K for a series of samples significantly differing in the volume fraction of the crystallites, allowed to characterize the temperature evolution of the properties of these two-phase magnets, in particular the effects occurring in the vicinity of the ferro- para-magnetic transition of the amorphous matrix. The critical temperature of this transition ranged from around 100 up to 140 K depending on the degree of divitrification.

Magnetic properties of a series of two-phase nanocrystalline magnets differing in the volume fraction of the crystallites, produced by partial devitrification of the Co-based metallic glass exhibiting low Curie temperature, were studied using ferromagnetic resonance (FMR) technique. The measurements were carried out in a range of temperatures from 4 to 300 K. Changes in the FMR-spectra were observed at the temperatures close to the Curie points of the residual amorphous matrix (100–140 K, depending on the annealing temperature) being correlated with the temperature dependence of magnetization. Well defined resonance lines observed at low temperatures became much broader and complex in the range of higher temperatures. The latter effects were interpreted in terms of the anisotropy of the single-domain particles. The calculated effective magnetizations and the g -factor appeared to be quite reasonable.

Co66Nb9Cu1Si12B12 metallic glass is used as the parent material for nanocrystalline magnets exhibiting low Curie temperature of the amorphous matrix (100–140 K). Two structural transformations of the as-spun alloy are identified during the annealing process. The microstructures created are related to magnetic properties of the nanocrystalline samples.

Co-Fe-Mo-Mn-Si-B metallic glass ribbon (Vitrovac 6030) was subjected to the isothermal annealing at temperatures in the range 523-873 K so as to produce a series of samples with gradually coarser microstructure. For this series of samples a giant increase in the coercivity, exceeding three orders of magnitude, is observed. This increase is interpreted in terms of the strengthening of the pinning effect of the nanocrystalline structure on the moving domain walls. It is shown that the anisotropy of the created crystallites is mainly responsible for the increase in the pinning force since the effective anisotropy seen by the wall becomes larger and larger with the gradual increase in the density and size of the grown particles. PACS numbers: 75.50.Cc, 75.50.Kj, 75.60.Ch

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.

Rapidly quenched Co-Nb-B-Cu metallic glasses, designated to investigate magnetic interactions between created nanocrystallites as well as magnetic properties of these particles themselves, have been chosen as the parent materials for nanocrystalline magnets with the Curie point of the amorphous matrix below the room temperature. The crystallization behavior as well as magnetic properties of the as-quenched alloys with different Co content were studied. The microstructure of the selected nanocrystalline samples obtained by the isothermal annealing of the as-quenched alloys are also presented.

Amorphous and nanocrystalline Fe-Zr-B-(Cu) alloys with different B content have been studied with the Mossbauer spectroscopy and differential scanning calorimetry. It has been shown that amorphous alloys show Invar type compositional characteristics whereas in the nanocrystalline state the residual amorphous matrix does not exhibit the exchange frustration due to enrichment with Zr and B. In the Mossbauer spectra of the nanocrystalline alloys, besides of the contributions from bcc-Fe and amorphous phases, an additional component is observed and attributed to the crystalline grain-amorphous matrix interfaces.

The nanocrystalline state of the formally amorphous alloy Fe73.5Cu1Nb3Si15.5B7 is achieved by a heat treatment at temperatures between 500 ° C and 600°C. The XANES and EXAFS methods were applied for investigation of local structure and chemical bonding around Fe atoms in amorphous and nanocrystalline alloys. The Fe K absorption spectra were measured in the transmission mode at room temperature for Fe73.5CuiNb3Si15.5B7 amorphous and nanocrystalline alloys and compared with the spectra for Fe metallic foil and Fe3Si polycrystalline samples.

It is shown that, besides the promising prospects of applications, nanocrystalline Fe-based metallic glasses (nominal composition Fe73.5Cu1Nb3Si13.5B9) are interesting objects for basic research because of the variety of magnetic phases which they can show at elevated temperatures. These unusual particulate media show ferromagnetic behavior for temperatures below the Curie point of the residual amorphous matrix, however, in the temperature range above this point they may display superferromagnetic or superparamagnetic properties depending on the size and volumetric fraction of the nanoparticles created within the material by the appropriate annealing. The results of a number of experiments are presented, which show that all the magnetic phases mentioned above can be created in the nanocrystalline material considered.

Annealing of the initially amorphous Fe66Cr8Cu1Nb3Si9B13 metallic glass above its crystallization temperature leads to the ultrafine crystalline structure of the bcc-FeSi solid solution with a relatively wide distribution of the particle sizes 9≤D≤35 nm. At elevated temperatures the magnetization curves no longer show hysteresis and ideal superparamagnetic behavior is observed. The kinetics of magnetic moment increase during the crystallization process at the time of annealing is also presented.

Experiments were performed on Co67Fe4Cr7Si8B14 metallic glass in which the transverse magnetic anisotropy was induced by a proper annealing process. Measurements of the magnetic permeability μ at high frequency of 20 and 200 kHz were performed versus tensile stress applied to the sample. It was found that for the low-stress region the value of the initial permeability increases with the stress but at higher stress, depending on the induced anisotropy, the behavior of μ can be significantly modified. The results obtained are interpreted as an influence of the stress-dependent modification of the domain pattern, as shown by the observation of the Kerr effect domain structure.

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.

FeZrBCu nanocrystalline materials obtained by controlled crystallization of the amorphous alloy are composed of bcc-Fe grains (10 nm in diameter) embedded in a residual amorphous matrix. In this article it has been shown that in such a mesoscopic system the interfaces exhibit identifiable properties that differ from those of the interior. In the Mossbauer spectra, besides of contributions from bcc phase and that of the residual amorphous matrix, an additional component was observed and attributed to the crystalline grain-amorphous matrix interfaces. The effect of the surface layer on the effective magnetostriction is also presented and discussed.

Co66Nb9Cu1Si2B12 metallic glass is used as a parent material for nanocrystalline magnets exhibiting low Curie temperature of the amorphous matrix (100–140 K). Precipitation of Co nanoparticles destroys the ferromagnetic ordering in the amorphous alloy and leads to a low-temperature cluster-glass state. At higher temperatures, the grains embedded in the paramagnetic matrix exhibit a superparamagnetic behaviour. In the fully crystallized state the magnetic properties of the material, composed of two crystalline phases with their Curie points above the room temperature, are mainly governed by the inter- and intra-phase magnetic interactions which lead to a preferential ferromagnetic ordering.

The experimental results of the magnetic anisotropy induced during annealing under tensile stress and/or longitudinal magnetic field in FeCrSiB metallic glasses are presented. The possible origins of the induced anisotropies are connected with the type of 3d metal atoms arranging into pairs during annealing.

It is shown that stress-anneal-induced magnetic anisotropy is created during annealing, prior to not after stress release. It is argued that the commonly used model of anelasticity, based on the microscopic mechanism of local bond reorientation gives a description which is inconsistent with the experimental results obtained.

Fe 81 P 1 Si 23 Nb 3 Cu 1 metallic glass is used as the parent alloy for a new soft magnetic nanocrystalline material. Two structural transformations of the as-cast alloy are identified during the annealing process. The microstructures created are related to magnetic properties of the nanocrystalline samples.

The nanocrystalline Fe66Cr8Cu1Nb3Si13B9 metallic glass with relatively low Curie temperature of the amorphous matrix has been proposed as a particulate medium showing superparamagnetic behavior at elevated temperatures. The samples of this material with different volumetric fractions of the crystalline phase, were characterized by differential thermal analysis, X-ray diffraction and transmission electron microscopy as well as by temperature dependencies of saturation magnetization and isothermal magnetization curves. The correlation between the structural parameters determined by direct measurements and those estimated from the magnetic studies is shown and discussed in terms of a new algorithm which allows to determine a distribution of the particle magnetic moments.

The expectation that the nanocrystalline Fe-based metallic glasses may show the richness of magnetic phases with a change of the temperature has experimentally been confirmed. It has been shown that, depending on the annealing conditions (resulting in controlled crystallite size as well as the volumetric fraction) the particles exhibit superparamagnetic or "superferromagnetic" behavior at elevated temperatures. In these cases, the amorphous matrix, into which the particles are embedded, is in paramagnetic state. In order to confirm the occurrence of these phases, magnetization characteristics measured at different temperatures were analyzed in terms of the well-known Langevin approach. At sufficiently low temperature (e.g., at room temperature), lower than the Curie points of both, the amorphous matrix and the particles, the sample behaves ferromagnetically in a way as it does for the typical commercial material.

The composition dependences of the basic magnetic properties indicate that Fe-rich FeZrB(Cu) amorphous alloys show behavior characteristic of Invar material. The critical Fe concentration at which the ferromagnetic order disappears is found to be 98%.

The Mossbauer spectra of FeZrB(Cu) amorphous alloys show a bimodal hyperfine field distribution with an additional low-field component, the relative intensity of which increases with decreasing boron content. The results are interpreted in terms of two different Fe local environments and the accompanying magnetic exchange frustration in Fe-rich regions.

Mossbauer spectroscopy has been performed over the temperature range 4.2–833 K in the nanocrystalline Fe 66 Cr 8 CuNb 3 Si 13 B 9 metallic glass. The sample was found to consist of α-(FeSi) crystalline phase with 14 at% Si embedded in a chromium enriched amorphous matrix. The Curie temperature of the matrix is found to be 403 K.

AC susceptibility measurements show that in Fe 89 Zr 7 B 4 amorphous material the ferromagnetic-reentrant spin-glass transition follows the paramagnetic-ferromagnetic transition as the temperature is lowered, whereas the behavior of nanocrystalline sample is characteristic of ferromagnetic material. The results are interpreted in terms of a non-collinear magnetic structure in amorphous alloy which changes considerably after crystallization.

The experimental results for the stress and/or field induced anisotropies in the Co-Fe-Ni-Si-B metallic glass are presented. The results were analyzed in order to find possible contributions to the observed anisotropies as well as to explain the so-called anisotropy “enhancement” effect.