Recoilless fraction, structural, magnetic and thermal properties of Fe73.5Cu1Nb3Si13.5B9 alloy

Differential scanning calorimetry, X-ray diffraction and room temperature Mössbauer spectrum measurements of Fe_73.5Cu₁Nb₃Si_13.5B₉ (Finemet) alloy have been carried out in order to study its structural and magnetic properties as a function of annealing temperature. The DSC profile of as-quenched Finemet showed two exothermic peaks at 530 and 702 °C, corresponding to two crystallization processes. The Finemet alloy remains amorphous at 450 °C with one broad peak in XRD pattern and one broad sextet in Mössbauer spectrum. When the Finemet alloy was annealed at 550 °C, only well indexed body-center-cubic phase was detected. After being annealed at 650 and 750 °C, the XRD patterns showed the coexistence of α-Fe(Si) and Fe-B intermetallic phases with the increase in XRD peak intensities, indicating the growth of crystallites and the decomposition of Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy at elevated temperatures. The Mössbauer spectra of annealed Finemet alloy could be fitted with 4 or 5 sextets and one doublet at higher annealing temperatures, revealing the appearance of different crystalline phases corresponding to the different Fe sites above the crystallization temperature. The appearance of the nanocrystalline phases at different annealing temperatures was further confirmed by the recoilless fraction measurements.     

Temperature dependence of the Mössbauer spectra of amorphous and nanocrystallized Fe86Zr7Cu1B6

Mössbauer measurements have been performed on amorphous and nanocrystalline alloy ribbons of nominal composition Fe₈₆Zr₇Cu₁B₆. The nanocrystalline samples were obtained by annealing the as-quenched alloy at different temperatures in the range between 650 and 870 K. Mössbauer spectra of the as-quenched amorphous sample have been recorded at 77 K, room temperature and above the Curie temperature (330 K) at 360 K. We have also performed Mössbauer measurements at room temperature in the nanocrystalline alloys to characterize the phases that appear after the annealing and their relative concentration. The as-quenched sample spectra reveal the existence of two inequivalent sites for Fe. Such a feature is also observed in the remaining amorphous phase of the annealed samples. In the first steps of crystallization, -Fe precipitates and its concentration increases with the annealing temperature. The experimental results suggest that the composition of the whole amorphous phase does not suffer large changes during crystallization.     

Mössbauer spectroscopy studies of spin reorientations in amorphous and crystalline (Co0.2Fe0.8)72.5Si12.5B15 glass coated micro-wires

Thermo-gravimetric, differential scanning calorimetry and comprehensive ⁵⁷Fe Mössbauer spectroscopy studies of amorphous and crystalline ferromagnetic glass coated (Co_0.2Fe_0.8)_72.5Si_12.5B₁₅ micro-wires have been recorded. The Curie temperature of the amorphous phase is T_C(amorp) ∼730 K. The analysis of the Mössbauer spectra reveals that below 623 K the easy axis of the magnetization is axial-along the wires, and that a tangential or/and radial orientation occurs at higher temperatures. At 770 K, in the first 4 hours the Mössbauer spectrum exhibits a pure paramagnetic doublet. Crystallization and decomposition to predominantly α-Fe(Si) and Fe₂B occurs either by raising the temperature above 835 K or isothermally in time at lower temperatures. Annealing for a day at 770 K, leads to crystallization. In the crystalline material the magnetic moments have a complete random orientation. After cooling back to ambient temperature, both α-Fe(Si) and Fe₂B in the glass coated wire show pure axial magnetic orientation like in the original amorphous state. The observed spin reorientations are associated with changes in the stress induced by the glass coating.     

Mössbauer study of isothermally annealed amorphous Fe-Nb-Cu-Si-B alloys

Amorphous ribbons of Fe_73.5Nb₃Cu₁Si_13.5B₉ have been annealed above the crystallization temperature. Annealed samples consisted of crystalline and amorphous phases in a wide temperature range. Two samples of different thicknesses of 33 µm and 27 µm were isothermally annealed at a temperature of 545°C from 0.5 to 5 h in a vacuum furnace. The amount of crystalline phase increases rapidly in the ticker sample. The crystalline part of the Mössbauer spectrum consists of four sharp sextets which can be assigned to a DO₃-structure FeSi alloy. After 700°C annealing the amorphous phase was not observed and the crystalline phase consisted of the DO₃-structure FeSi alloy, paramagnetic FeNbB and presumably Fe₂₃B₆ and Fe₃SiB₂.     

XRD, HRTEM, magnetic and Mössbauer studies on chemically prepared Fe-doped nanoparticles of cerium oxide

Nanocrystalline samples of Fe-doped cerium oxide (Ce_0.90Fe_0.1O₂) are prepared by sol-gel method. The precursor materials used for the synthesis are ferric nitrate and cerium nitrate. The as-prepared samples is annealed at different temperatures to obtain the sample with different particle sizes. The crystallographic phases of the nanocrystalline materials have been confirmed by X-ray diffractograms (XRD). The sizes of the nanoparticles estimated from the peaks of the XRD patterns using Debye-Scherrer equation are in the range 6-58 nm. Results extracted from the high-resolution transmission electron microscopy (HRTEM) are in agreement with the findings obtained from XRD. The average magnetic susceptibilities of all the samples with different particle sizes are measured in the temperature range 300-14 K. The average susceptibilities of the samples annealed below ∼740 °C show paramagnetic behaviour. The susceptibilities of the samples annealed at and above ∼740 °C sharply decrease at ∼240 K and this sharp transition is quite likely due to the anti-parallel alignment of Fe³⁺ spins and is attributed to Morin transition of α-Fe₂O₃. Mössbauer spectra of the samples annealed at and above ∼740 °C give sextet patterns indicating the presence of exchange interaction among the Fe³⁺ ions of these samples and these sextets are also of typical nature of the α-Fe₂O₃ phase. The Mössbauer spectra of the samples annealed below ∼740 °C are doublets which may be attributed to either superparamagnetic and/or paramagnetic type nanoparticles.     

Thermal stability of Fe3Si-based nanocrystals

We studied the thermal stability of nanocrystalline (Fe₃Si)_0.95Nb_0.05 and Fe₃Si alloys prepared by high-energy ball milling. Alloys were characterized by Mössbauer spectrometry, as well as X-ray diffractometry and transmission electron microscopy. The Nb-containing alloy was considerably more stable against grain growth than was the binary Fe₃Si alloy. Mössbauer spectrometry showed that the Nb atoms segregated away from the DO₃ ordered domains, probably to grain boundaries, and thus provided a strong suppression on grain growth.     

Characterization of phases in the Fe-Nb system

The Fe-Nb system was investigated by means of X-ray diffraction and Mössbauer spectroscopy (at 300 and 77 K), in the range from 1 to 66.7 at%. We have found that the limit of solubility of Fe in Nb at 1100°C is between 3 and 4 at% Fe, and observed the coexistence of the Nb solid solution (Nbss) phase and Fe₂₁Nb₁₉ in the range from 4 to 40 at% Fe. The Mössbauer parameters of all the single phases are reported. The lattice parameters of Nbss phase present no significant variation with the Nb content. The X-ray pattern for the Fe₂₁Nb₁₉ phase could not be solved. The Laves phase Fe₂Nb presents Mössbauer and X-ray parameters that agree with the literature.     

In situ Mössbauer and magnetization studies of Fe–Si nanocrystallization in Fe73.5Si13.5B9Cu1Nb1 X2, with X = Nb, Zr, Mo, amorphous alloys

The Fe–Si nanosized particles were obtained by controlled partial crystallization of Fe_73.5Si_13.5B₉Cu₁Nb₁X₂ (X = Nb, Zr, Mo) amorphous alloys. In situ Mössbauer spectroscopy and magnetization measurements have been used to follow the temperature-dependent magnetization of the amorphous as well as of the nanosized Fe–Si particles. Our results, for the residual amorphous and of nanoparticles phases, show that the temperature dependence of the hyperfine field and magnetization of both residual amorphous and nanocrystalline Fe(Si) phases are different from that of the as-quenched bulk amorphous or crystalline Fe₃Si alloys. Likewise, from the temperature dependence studies it was possible to determine that the onset temperature of the nanocrystallization process increases in the sequence Mo < Nb < Zr, for the same annealing conditions.     

Mössbauer studies of the relaxation in the FeNiB amorphous system

Young's modulus of Fe₄₄Ni₃₈Bi₁₈ amorphous ribbons annealed at different temperatures shows an oscillating behavior depending on the annealing temperature. In a previous work, several samples were studied and the Young modulus was correlated with the hyperfine field distributions. In this work, more samples are analyzed and further Mössbauer studies are performed in order to verify the above-mentioned correlation.     

Changes in the hyperfine interactions in the Fe80Nb3Cu1B16 metallic glass under tensile loading

The influence of tensile stress on the changes in hyperfine parameters obtained by Mössbauer spectroscopy of the ferromagnetic amorphous NANOPERM-type Fe₈₀Nb₃Cu₁B₁₆ alloy has been investigated. The bulk changes are obtained by Mössbauer spectroscopy in a transmission geometry using γ-rays; the surface properties are studied in a scattering geometry using conversion electrons. The Mössbauer spectra are analyzed by two distributions of hyperfine inductions, which result in high-field and low-field components corresponding with a model of clusters formed by predominantly iron atoms and intermediate phase containing mainly the Nb, Cu and B atoms. The obtained results are completed by the bulk and surface magnetic measurements, with observations of surface morphology by AFM and microstructure by SEM. The investigations yield approximately linear increase of hyperfine parameters and slight deterioration of the bulk as well as surface magnetic characteristics with tensile loading.     

Magnetostatic properties of K2Co x Fe1−x F4, a system with competing anisotropies

The magnetostatic properties of K₂Co _x Fe_1–x F₄ have been investigated by susceptibility and Mössbauer measurements at different concentrations and temperatures. Three magnetically ordered phases are found: a planar phase, an OAF phase, and an uniaxial phase. The experimental results are compared to a molecular-field calculation. At certain concentrations and temperatures it is not possible to obtain a good least squares fit of the Mössbauer spectra, which is tentatively assigned to relaxation effects due to fast spin fluctuations at the OAF phase transition.     

Mössbauer and X-ray diffraction studies of mechanically alloyed Fe-Al

Powder samples of Fe₂₅Al₇₅ were prepared by the mechanical alloying method. Mössbauer effect, X-ray diffraction and DSC measurements indicate that Fe and Al crystalline powder transform into Fe-Al amorphous powder with increasing milling time. The X-ray diffraction patterns of the milled Fe₂₅Al₇₅ do not clearly show a sign of the existence of the intermetallic phases or Fe-Al solid solution. However, Mössbauer measurements reveal two sites with hyperfine magnetic fields 30.2 and 26.0 T. These sites form locally during the milling process and then they disappear.     

Mössbauer study of YBa2(Cu1−x Fex)3Oy from an aspect of distribution of Fe

Fe Mössbauer spectra have been measured systematically in YBa₂(Cu_1–x Fe_x)₃O_y prepared by two different heat treatments: the usual treatment (O) and the heat treatment including that under lower oxygen fugacity at high temperatures followed by the oxidation process at low temperatures (NO). From the analysis of the results in terms of binomial random probability, it has been found that the Fe distribution in the Cu(1) site is almost random in the heat treatment (O). Here, the D1 and D2 components in the Mössbauer spectra, which have been assigned to the 4 and 6 oxygen coordinated Fe ions in the Cu(1) site respectively, should correspond to the monomer and cluster Fe ions. In the heat treatment (NO), some of the Fe ions are transferred to the Cu(2) site and there exist only cluster Fe ions in the Cu(1) site, resulting in the characteristic change of macroscopic properties of this system.     

Structural relaxation of FeNiB amorphous alloy

Young's modulus was measured in rapidly quenched ribbons of Fe₄₄Ni₃₈B₁₈ annealed at a rate of 5 K/min up to different temperatures. An oscillating behavior was observed. Samples annealed up to temperatures that correspond to maxima and minima values of Young's modulus were studied with Mössbauer spectroscopy in order to correlate the macroscopic parameter with the hyperfine field distribution.     

Effects of annealing temperature on structure and magnetic properties of amorphous Fe61Co27P12 nanowire arrays

Arrays of Fe₆₁Co₂₇P₁₂ nanowire with an aspect ratio about 70 were prepared in anodic aluminum oxide templates by electrodeposition. The influences of annealing temperature on structure and magnetic properties of Fe₆₁Co₂₇P₁₂ nanowires were studied. When the specimens were annealed below 400 °C, there are no obvious changes in structure except relaxation. With the annealing temperature increasing from 400 to 600 °C, the Fe-Co phase is detected by X-ray diffraction and Mössbauer spectra. The crystalline fraction and hyperfine field can be derived from Mössbauer spectra. The room temperature magnetic hysteresis loops show that the coercivity and squareness of the nanowire arrays in parallel to the wire axis increase with the increasing of annealing temperature, which mainly attributes to the strengthening of anisotropy.     

Phase analysis of hard magnetic Nd4Fe77B19 ribbon

Amorphous Nd₄Fe₇₇B₁₉ ribbon was prepared by conventional single-roller technique. Room temperature transmission⁵⁷Fe Mössbauer spectra were taken in the as-prepared state and after annealing 650°C/30 min in N₂-atmosphere and compared with that of the crystalline master alloy. The broad hyperfine induction distribution in the amorphous state was fitted by two symmetric Gaussians reflecting its asymmetry. In the annealed state, the spectrum decomposes into a series of sharp sextets corresponding to -Fe (6%), Nd₂Fe₁₄B (38%) present also in the master alloy, tetragonal Fe₃B (39%) and probably an inter-grain remainder (17%). No traces of the Nd₂Fe₁₇ admixed in the master alloy were found in the crystalline state. The results of the Mössbauer spectroscopy are compared with those of the X-ray and magnetic methods.     

Structure and magnetic properties of FeMnAl alloys investigated by Mössbauer spectroscopy and X-ray diffraction

The system (Fe_0.88Mn_{0.12 1–x} Al _x has been investigated in a concentration range from 5 to 14 at.% Al. We applied Mössbauer spectroscopy in the temperature range from 4 up to 900 K and X-ray diffractometry at room temperature. The as-cast samples show a bcc phase for all concentrations and exhibit broadened six-line Mössbauer spectra typical for disordered alloys. The Mössbauer spectra during a high temperature treatment show dramatic changes. These are due to ordering processes appearing at temperatures above 700 K. As an example of the observed changes, we present results obtained for the alloy withx= 14 at.% Al.     

FINEMET type alloy without Si: Structural and magnetic properties

Magnetic and structural properties of a Finemet type alloy (Fe_73.5Ge_15.5Nb₃B₇Cu₁) without Si and high Ge content were studied. Amorphous material was obtained by the melt spinning technique and was heat treated at different temperatures for 1 h under high vacuum to induce the nanocrystallization of the sample. The softest magnetic properties were obtained between 673 and 873 K. The role of Ge on the ferromagnetic paramagnetic transition of the as-quenched alloys and its influence on the crystallization process were studied using a calorimetric technique. Mössbauer spectroscopy was employed in the nanocrystallized alloy annealed at 823 K to obtain the composition of the nanocrystals and the amorphous phase fraction. Using this data and magnetic measurements of the as-quenched alloy, the magnetic contribution of nanocrystals to the alloy annealed at 823 K was estimated via a linear model.     

Radio-frequency induced effects in amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9

The rf collapse and sideband effects are used to study the microstructure of the Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy in the amorphous and nanocrystalline state. Nanocrystalline grains of -Fe(Si) are formed as a result of annealing of the amorphous alloy at 520–570 °C. The results show that the complete rf collapse of magnetic hfs in the Mössbauer spectra occurs only in the amorphous phase. The rf collapse is strongly affected by the onset of the nanocrystalline phase and is suppressed when the Fe₃B and Fe₂B phases are formed. Partial collapse allows us to follow the remaining crystalline fractions during the crystalline process. The rf sidebands disappear due to the formation of nanocrystals because of the vanishing magnetostriction.