Some magnetic properties of nanoperm alloy after irradiation

Transmission⁵⁷Fe Mössbauer spectrometry was used to study the microstructural and magnetic changes induced by neutron irradiation of nanocrystalline Fe-Zr-B alloy. Measurements were performed in the temperature range from 77 K up to 500 K. The evolutions of both the hyperfine field distribution, the average hyperfine field value, the mean orientation of the ferromagnetic domains and the value of the Curie temperature are consistent with short-range atomic order changes resulting from the neutron irradiation damages. In addition, the neutron irradiation affects significantly the proportions of amorphous, crystalline and interfacial phases. The results of Mössbauer spectrometry were correlated with those obtained by X-ray diffraction.     

Nanocrystalline iron-based alloys investigated by Mössbauer spectrometry

Nanocrystalline alloys exhibit great fundamental and technological interests because of their microstructural properties, and their excellent soft magnetic properties. ⁵⁷Fe Mössbauer spectrometry is a well suitable technique to investigate Fe-based nanocrystalline alloys: its local probe behaviour permits to elucidate the nature of hyperfine interactions at different resonating iron nuclei and to distinguish their immediate atomic surroundings. We review on the recent Mössbauer developments performed on first FeCuMBSi and then FeCuBSi nanocrystalline alloys. From Mössbauer studies, one can estimate the crystalline (i.e., amorphous) fraction, the Si-content in Fe--Si nanocrystalline grains emerging from amorphous alloys of the first series, the temperature dependence of magnetic behaviours of both crystalline and amorphous phases; finally, we present a novel fitting procedure applied to FeCuBSi nanocrystalline alloys which result from bcc-Fe crystalline grains embedded in an amorphous matrix. In this case, the hyperfine structure is able to model the intergranular phase.     

Progress of laser spectroscopy at the IGISOL

Magnetic interactions and microstructure in the amorphous and nanocrystalline Fe₉₀Zr₇Cu₁B₂ alloy were investigated. These studies were carried out in the temperature range from 140 up to 380 K, using a Mössbauer spectrometer and completely automated set-up for measurements of magnetic properties. It has been found that the Curie temperature and quadrupole splitting decrease after annealing the sample at 573 K for 1 h (invar effect). However, this behaviour is not observed in nanocrystalline samples. In the early stages of crystallization (the volume fraction of the crystalline phase equal to about 0.06) α-Fe grains above the Curie temperature of amorphous matrix may be treated as non-interacting particles. The particle size estimated by Mössbauer spectra and magnetization curve analysis is equal to about 4 nm.     

Nanocrystalline alloys of Fe-Cu-Nb-Si-B after neutron irradiation

Transmission Mössbauer spectroscopy was used to study changes induced by irradiation of amorphous and nanocrystalline samples. In an as-cast sample neutrons mostly affect the orientation of a net magnetic moment. The average hyperfine field decreases towards higher neutron fluencies. In the case of the nanocrystalline samples a new disordered structure is created in the amorpous remainder corresponding to boride phases as it is shown in the samples isothermally heated from 1 to 8 hours. The structural changes of the amorphous remainder depend on the stage of crystallization and total neutron fluencies.     

Magnetism of nanocrystalline materials

Nanocrystalline solids are materials consisting of small crystallites (typically 1–10 nanometers). These materials have a high proportion of atoms located in the interfacial regions between the crystallites. Therefore their magnetic properties are strongly determined by the interfaces. In this work we present Mössbauer studies carried out on various nanocrystalline materials. Beneath the normal crystalline component the Mössbauer spectra clearly indicate the existence of an component with modified magnetic properties which corresponds to the interfaces in this type of material. For nanocrystalline α-Fe an enhancement of the hyperfine field was observed in the interfacial component at low temperatures, whereas a decrease was found for nanocrystalline Ni.     

How can Mössbauer Spectrometry Contribute to the Characterization of Nanocrystalline Alloys?

A controlled annealing of amorphous precursors represents a simple way of obtaining nanocrystalline alloys featuring interesting magnetic properties suitable for technical applications. They stem from the presence of crystalline nanograins embedded in the amorphous residual matrix which determine the resulting macroscopic parameters. In order to understand correlation between the microstructure and the resulting magnetic behaviour, Mössbauer spectrometry is used as a method of local probe analysis. Possibilities of this technique are discussed and representative examples of investigation of NANOPERM-type nanocrystalline alloys are provided.     

Iron-based nanocrystalline alloys investigated by 57Fe Mössbauer spectrometry

Soft magnetic nanocrystalline alloys have attracted great fundamental interest in recent years due to their two-phase structural and magnetic behaviour. We review first the reliability of the fitting procedures of spectra obtained by ⁵⁷Fe Mössbauer spectrometry which is a very efficient tool to investigate such materials. Then, we report the common features which characterise the temperature dependence of Mössbauer spectra; the hyperfine field temperature dependence of both the crystalline grains and the intergranular phase is discussed for different crystalline fractions in order to model the magnetic behaviour of the nanocrystalline alloys.     

Magnetic hyperfine properties in FeZrB‐type nanocrystalline metallic alloys

Transmission Mössbauer spectra were performed on FeZrB nanocrystalline alloys with high crystalline fraction (≈60%)at temperatures comprised within the range 77–600 K. We report the temperature dependencies of the magnetic hyperfine data of the three contributions: the crystalline bcc‐Fe grains, the residual amorphous phase, and the interface intermediate between the bulk of crystalline and amorphous phases. The evolution of the average value of the hyperfine field characteristic of the residual amorphous phase is discussed in terms of interactions between crystalline grains transmitting through the intergranular phase.     

Magnetic and Mössbauer Studies of Fe<Subscript>76</Subscript>Mo<Subscript>8</Subscript>Cu<Subscript>1</Subscript>B<Subscript>15</Subscript> Nanocrystalline Alloy

The influence of different degrees of crystallinity on the magnetic behaviour of heat-treated nanocrystalline Fe₇₆Mo₈Cu₁B₁₅ alloy has been investigated using a combination of Mössbauer spectrometry and magnetic measurements. The evolution of magnetically active regions and their growth with rising contents of nanocrystals are followed by distributions of hyperfine interactions. Combined electric quadrupole and magnetic dipole interactions corresponding to non-magnetic and magnetic regions inside the amorphous phase, respectively, were revealed. A deterioration of the soft-magnetic properties takes place for the samples exhibiting low fraction of crystallinity. The very good soft-magnetic behaviour is regained for the samples where the primary crystallization process is almost finished.     

Structure and Dynamics of High-Z Ions Studied at the ESR Storage Ring

Hyperfine Interactions - The magnetic order and crystallization of the amorphous Fe75Si15B10 alloy prepared by mechanical alloying was studied in situ by 57Fe Mössbauer spectroscopy. These...     

Influence of the Swift Heavy Ion Irradiation on the Short Range Order in Amorphous FeNiSiB Alloys

The influence of the high-energy heavy ion irradiation on the short range order and magnetic texture in amorphous FeNiSiB alloys are studied by Mössbauer spectroscopy. The rf-Mössbauer measurements reveal clear changes of the local structure induced due to high electronic energy deposition and related to the anisotropic growth effect. In the substantial volume fraction of irradiated samples the spins change their orientation from the in-plane to the perpendicular one.

     

Mössbauer spectroscopy of Fe-based nanomaterials

X-ray diffraction, magnetic measurements and Mössbauer spectroscopy were used to study magnetic properties and hyperfine interaction parameters of nanocrystalline (< 10 nm) and bulk bcc Fe, Fe₉₀Ge₁₀, and Fe₇₇Al₂₃ alloys. It has been established that nanocrystalline state does not influence the formation of specific saturation magnetization, Curie temperature, isomer shift and hyperfine magnetic field. No additional sextets in Mö ssbauer spectra as well as special features in temperature dependences of a.c. magnetic susceptibility have been found. A slight increase (～ 20%) of the width of the nanocrystalline Fe Mössbauer spectral lines has been observed.     

X-Ray Diffraction,Mössbauer and Magnetization Studies of Nanocrystalline Fe33Ge67 Alloy Prepared by Mechanical Alloying

Hyperfine Interactions - The nanocrystalline Fe33Ge67 alloy was prepared by mechanical alloying and its formation was followed by X-ray diffraction, 57Fe Mössbauer spectroscopy and...     

Effect of aluminum on the hyperfine field and crystallization behaviour of NANOPERM alloy

The effect of Al on the hyperfine fields and crystallization of NANOPERM alloy has been studied by introducing 2% Al for Fe in Fe₈₈Zr₇B₄Cu₁. Al is found to enhance the nucleation rate in these alloys. Mössbauer spectroscopic technique has been used to trace the effect of Al on the hyperfine interactions in the amorphous and nanocrystalline state of these alloys. The hyperfine field clearly shows the presence of Al both in the amorphous and the nanocrystalline phase. Magnetic measurements using VSM and also XRD, TEM and DSC studies have been used to support the conclusions derived using Mössbauer spectroscopy.     

Irradiation effects in amorphous alloy Fe80B20

The Mössbauer effect has been used to study the irradiation effects in the amorphous alloy Fe₈₀B₂₀ after 40 keV helium ion bombardment. Conversion electron Mössbauer spectroscopy reveals the eminent irradiation effects; α-iron phase appears in the damaged region of the sample.     

Nanogranular Phase Formation During Devitrification of Fe(NiCo)ZrB Amorphous Alloys

A comprehensive review of our recent experimental and theoretical developments in the processing of nanocrystalline soft magnetic materials made by crystallization of amorphous precursors and containing new nanocrystalline phases is given. The relationship between the structures of the metastable and equilibrium phases and their transformations are discussed. Nickel-rich amorphous precursors with stoichiometry Ni₆₄Fe₁₆Zr₇B₁₂Au₁ were produced by melt-spinning technique and then heat-treated at temperatures ranged from 420 °C to 600 °C for one hour to form nanostructured alloy. The transformation from the amorphous state into the nanocrystalline state was investigated by the differential scanning calorimetry (DSC), the x-ray diffraction (XRD), the vibrating sample magnetometry (VSM) and Mössbauer techniques. The annealing favours the emergence of cubic Fe_xNi_23-xB₆ crystalline grains (10-25 nm in diameter). Magnetic measurements made at 4.2-1100 K reveal rather high value of saturation magnetization (nearly 60 and 40 Am²/kg at 4.2 K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300 K ⁵⁷Fe Mössbauer results which are well supported by the calculations of Ni and Fe magnetic moments in Ni₂₃B₆ and Fe₂₃B₆ phases, using the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. However, anomalous high magnetic moments of Fe and Co atoms were found in some inequivalent positions in the crystal structure.     

Mössbauer study of magnetic anisotropy in electrochemically deposited Fe−Ni−P amorphous alloys

In a previous work [1], a large magnetic anisotropy was found as a preliminary result of the formation of electrochemically deposited Fe₉₃P₇ alloy. Mössbauer spectroscopy was used in order to get information about the magnetic anisotropy of electrochemically prepared Fe?P and Fe?Ni?P amorphous alloys. The Mössbauer spectra and the hyperfine field distributions of the samples show that Fe?Ni?P and Fe?P electrodeposited amorphous materials can be prepared in a reproducible way from a point of view of short range ordering which is strongly dependent on the chemical composition determined by preparation conditions. The average magnetization directions in the samples were determined from the transmission spectra measured in a normal and two tilted geometries by two types of evaluation methods [2,3]. We have found that the small spread model of the domain structure better describes the experimental results. The obtained data reflect the prevailing anomalous magnetization orientation in these electrodeposited amorphous alloys.     

Nanostructured Y-Fe Alloys Produced by Ball Milling

Ball milling was used to produce nanostructured Y-Fe alloys. Depending on preparation conditions, nanocrystalline and amorphous components are formed to coexist. The transmission Mössbauer spectra exhibit YFe₂ and amorphous components. The influence of superparamagnetic YFe₂ particles was separated from the amorphous part by measuring at 77 K. The thermal stability of the samples and the growth of equilibrium phases was studied by annealing.     

Structural and magnetic study of Mo-doped FINEMET

In this paper, a study of the structural and the magnetic correlation of the crystalline and amorphous phases in the nanocrystalline system Fe_73.5Si_13.5B₉Nb_3?xMo_xCu₁ (x=0, 1.5, 2, 3) was made. By means of Mössbauer spectroscopy, simple mass balance considerations and density measurements, both phases fractions and chemical compositions were calculated (in at%, wt% and vol%). Then, quasistatic magnetic measurements and ab initio calculations were used in a magnetic balance model in order to estimate the magnetic contribution of the remaining amorphous phase, which was compared to that of as-quenched amorphous samples of the same composition. The difference in both magnitudes showed the influence of penetrating fields and that these became more important for higher crystalline fractions.     

Electrochemical behaviour of electrodeposited Fe—8P amorphous alloys

Mössbauer spectroscopy was used in order to study the influence of electrochemical behaviour of electrochemically deposited Fe—8P amorphous alloy. Electrochemically deposited amorphous samples were exposed to corrosion in the solution of H₂SO₄ and Na₂SO₄ containing NaHSO₃ at pH=3.5. CEM spectra of as-deposited samples exhibit a typical sextet of ferromagnetic amorphous state. Even with samples being kept under corrosion condition for 10 minutes, the Mössbauer spectra reveal an extra Fe(III) component.