Hyperfine Magnetic Field Distribution Research Articles

Mössbauer effect study of γ-FeMn alloys

The disordered antiferromagnetic γ-FeMn alloys in the range of Mn concentration from 0 up to 50 at.% Mn were investigated by means of X-ray diffraction analysis (XRD), differential scanning calorimeter (DSC) and Mossbauer spectroscopy (ME) at room temperature and at 80 K. The lattice parameter is constant for Mn contents below 27 at.% and increases linearly for higher Mn concentration. The RT Mossbauer spectra for the alloys with less than 20 at.% Mn were fitted with quadrupole splitting (QS) distribution, and above 20 at.% Mn they were fitted with magnetic hyperfine field (HF) distribution. The averageQS decreases, while the HF maintain a constant value by increasing the Mn concentration. At 80 K, the HF increases linearly up to 30 at.% Mn and then maintains a constant value at about 38 kOe. The peak of the specific heat (c p) at the Neel temperature changes from broad to sharp as the Mn content increases. The Neel temperature increases with Mn concentration.

Mössbauer effect study of the as-quenched, annealed and crystallised Fe 85−xCr xB 15 metallic glass

57Fe Mössbauer effect study of the as-quenched, annealed and crystallized Fe 85− x Cr x B 15 metallic glasses with x = 1, 3, 5 and 8 has been performed. The fitting of the room-temperature Mössbauer spectra of the as-quenched alloys shows that the values of both the most probable and average magnetic hyperfine fields decrease rapidly at a rate of 23 kOe per at% Cr. The magnetic hyperfine field distributions exhibit bimodal structure for the 8 and 10 at% Cr compositions. The opposite trend observed in the variation of the Mössbauer hyperfine parameters with annealing temperatures for the Fe 80W 5B 15 and Fe 80Cr 5B 15 metallic glasses may be due to the effect of different magnetic behaviours of W and Cr. It also implies that the dense random packing structure in the two alloys is different. Mössbauer effect studies of the alloys crystallised at 1073 K for an hour reveal the growth of the precipitated α-Fe and σ-(Fe, Cr) crystalline phases with increase of Cr concentration.

Short range order at the surfaces of annealed amorphous Fe40Ni40P14B6 ribbons

Conversion electron Mossbauer spectroscopy (CEMS) and gamma transmission Mossbauer spectroscopy were used to measure the effects of annealing at 583 K in vacuum into about 200 nm thick layer below the two surfaces and on the bulk of theFe40Ni40P14B6 amorphous ribbons prepared by means of melt-spinning technique. The results show a large distribution of hyperfine magnetic fields on the bulk and in the surfaces of the samples. By means of selective analysis of hyperfine magnetic field distribution, we have evalueded the correlation between the different degree of short range orders at the surfaces and in the bulk of the samples, and the phosphorus segregation associated with mechanical cubrittlement induced at low annealing temperature.

Vapor quenched Ag 1- xFe x alloys: in situ Mössbauer studies

Metastable alloys of Ag 1- x Fe x ( x = 0.17, 0.30, 0.50, 0.54, 0.56, 0.80 and 1.0) were prepared by vapor condensation onto kapton substrates maintained at low temperature. The X-ray diffraction spectra of all Ag/Fe samples, with x<0.56, suggested the formation of a fcc structure with a very small grain size. The present work reports in situ Mössbauer measurements on Ag-Fe films and occurence of aging effects. All the spectra obtained at 5.5 K show magnetic hyperfine field distributions characteristic of disordered alloys and also texture effects. The results for composition dependence of lattice parameters and average hyperfine fields are compared with values reported in the literature for films prepared in different conditions.

Magnetic Mössbauer spectra observed in superconducting samples of YBa 2(Cu 1− xFe x) 3O 6.5+ p

Magnetic Mössbauer spectra have been observed at low temperature for samples of YBa 2(Cu 1− x Fe x ) 3O 6.5+ p with Fe levels x = 0.01, 0.02, 0.04, 0.10 and 0.20. Fits to these complex magnetic spectra were constrained by simultaneous fitting of low temperature magnetic and high temperature nonmagnetic spectra of the same sample. The fits revealed two magnetic components, an Fe 3+ magnetic sextet most prominent at x = 0.20 and, for smaller values of x, a complex component whose fitting required a distribution of magnetic hyperfine fields. The temperature dependence of the hyperfine fields of this latter component gave values of T hf where the magnetic hyperfine field appears.

Annealing studies of ultrafine amorphous Fe-B alloy particles

Mössbauer spectroscopy studies of the annealing of amorphous Fe 74B 26 shows that the width of the magnetic hyperfine field distribution decreases for annealing temperatures below 600 K. This is ascribed to structural relaxation of the amorphous phase. Annealing at higher temperatures leads to crystallization into α-Fe and Fe 2B with the intensity of the latter component decreasing with increasing annealing temperature. At 778 K only about 4 at% of boron is left in iron-containing phases. Most probably borates form at the expence of Fe 2B.

In situ Mössbauer studies of vapor quenched Ag/Fe and Au/Fe films

Metastable alloys of Ag1-xFex (x=0.17, 0.30, 0.50, 0.54, 0.56 and 1.0) and the stable Au1-yFey (y=0.18 and 0.25) alloy were prepared as thin films by vapor quenching method on low temperature kapton substrate. The X-ray diffraction spectra of all Ag/Fe samples. withx<-0.56, have indication of fee structure with very small grain size. The present work reports in-situ Mossbauer results on Ag/Fe and Au/Fe films. The spectra obtained are characteristic of homogeneous disordered alloy with broad magnetic hyperfine field distribution. Aging effect inducing cluster formation was observed in Ag/Fe films after they were heated to room temperature, but this behavior was not detected in Au/Fe samples.

Hyperfine interactions in amorphous Co 70− xNi xFe 5Si 15B 10 studied by the Mössbauer technique

The hyperfine interactions in amorphous Co 70− x Ni x Fe 5Si 15B 10 alloys are studied by means of the Mössbauer spectroscopy technique. The magnetic hyperfine field distributions, p( H), as well as average values of the quadrupole splitting and isomer shift measured at room temperature are presented. Quadrupole splitting shows no substantial dependence on the alloy composition. On the contrary, the peak in the p( H) shifts towards lower values with increasing nickel content, and the p( H) distributions broaden. The isomer shift increase with Ni concentration. It is concluded that the substitution of Co by Ni does not change the structure of the alloy, while it influences its electronic and magnetic properties. In particular, the number of delocalized electrons is decreasing with increase of Ni concentration. It is shown that in order to explain the asymmetries of the shape of the spectra observed an anisotropic interaction among 3d spins has to be assumed. The iron magnetic moments are slightly tipped out of the ribbon's plane.

Ordering and magnetic hyperfine fields in Pt3Mn0.9Fe0.1 studied by Mossbauer spectroscopy

The influence of structural defects on the magnetic properties of Pt3Mn0.9Fe0.1 are studied by means of Mossbauer spectroscopy. The magnetic hyperfine field distribution shows that the sample exhibits an inhomogeneous magnetization distribution. The cold work introduces a number of antiphase boundaries dividing the sample into subvolumes with the linear dimensions of 30-100 AA. The magnetization of these subvolumes performs a superparamagnetic-like relaxation. The origin of relaxation is discussed.

Mixed hyperfine interactions in amorphous materials: A model study

57Fe Mossbauer absorption profiles were calculated supposing distributions of all hyperfine parameters: hyperfine magnetic fields, isomer shifts, and electric field gradients. The effect of mixed hyperfine interactions was taken into account in all orders of perturbation theory. The shapes of the spectra were systematically studied for varying average values and widths of the hyperfine magnetic field distribution (HMFD). From the simulated spectra, the shapes of the HMFD were reconstructed using standard techniques of Mossbauer spectra processing which neglect the effects of random isomer shifts and electric field gradients. It has been shown that the reconstructed shapes of the HMFD differ qualitatively from the original single-peaked distributions and exhibit a double-peaked structure similar to the distributions found in many experiments on amorphous alloys with low iron content. A brief review of various mechanisms responsible for either apparent or real double-peaked structure of HMFD has been given.

Magnetic hyperfine field distribution in pyrrhotites from Mössbauer spectroscopy

Mossbauer spectra from intermediate pyrrhotite (Fe1−xS) samples were interpreted according to their hyperfine magnetic field distribution functions at the Fe nuclei in these sulfides. Seven non-equivalent Mossbauer sites for Fe were distinguished by their peak positions in the distribution functions obtained.

The Distribution of Magnetic Hyperfine Fields in Iron-Boron Amorphous Alloys Containing Transition Elements

The Distribution of Magnetic Hyperfine Fields in Iron-Boron Amorphous Alloys Containing Transition Elements

Hyperfine and X-ray investigations of amorphous Fe2Er and Fe2Ce alloys and the effect of hydrogenation on short-range order

The effect of hydrogenation on the short-range order of amorphous Fe2Er and Fe2Ce alloys has been investigated by Mossbauer, X-ray and magnetization measurements. The hydrogenation leads to drastic changes in the short-range order. The results of Mossbauer measurements show two different distributions of magnetic hyperfine fields for amorphous Fe2CeH4 alloys (a-Fe2CeH4). For a-Fe2ErH3 alloys we found drastic changes in magnetic structure, which is different from the well-known magnetic structures.

Short range ordering in undercooled Fe3Al

Alloys of Fe-27 at.% Al were prepared far from thermodynamic equilibrium by ultra-rapid quenching from the melt. The hyperfine magnetic field (hmf) distribution revealed a wide variety of local Al environments around57Fe atoms. Upon low temperature annealing, the probabilities of these different Al environments changed at different rates. The “kinetic path” of short range ordering in Fe3Al is consistent with that found in a previous study of long range ordering, where B2 order grows more rapidly than D03 order at lower temperatures.

Mössbauer isomer shift and hyperfine fields of ordered and disordered Fe3Al alloys

The Mossbauer technique was used to measure the hyperfine magnetic field and isomer shift of57Fe nucleus in the ordered and disordered Fe3Al alloys. The Mossbauer spectra were analyzed to yeld the hyperfine magnetic field distribution curves. A linear correlation has been revealed between the average hyperfine field and the average number of Al atoms in the first two nearest neighbour shells of57Fe nucleus,N Al, for both ordered and disordered alloys. The measured values of the mean isomer shift agree very well with the values expected from the Miedema-Van der Woude model.

Mössbauer effect and NMR studies of copper-cadmium ferrites

Hyperfine magnetic field distributions have been observed at room temperature in Cd x Cu1−xFe2O4 (0≤x≤0.5) ferrites by the Mossbauer and NMR methods and are explained by statistical distributions of metallic ions separately within A and within B crystal sublattices.

On the hyperfine magnetic field distribution at118Sn in spinel ferrites

The distributionP(H) of the hyperfine magnetic fieldsH at the119Sn nucleus in spinel ferrites can be reliably obtained by means of the decomposition method [10] adapted for this case. To interpretP(H), a polynomial model is proposed which accounts for the contribution inH of the magnetic ions in both octahedral (B) and tetrahedral (A) sites.

Magnetic properties of amorphous alloys based on Fe depending on composition and temperature investigated by means of Mössbauer spectroscopy

The subject of our study is the dependence of the hyperfine magnetic field H in metallic amorphous alloys of the type Fe 80− x TM x B 20 (TM ≡ transition metal, x ≡ content of TM ) on the atomic number Z of TM and on temperature T. We us ed Mössbauer spectroscopy for these investigations. Mössbauer spectra were analysed by means of computer methods using Window's program. Over a half of these spectra were verified by using Hesse-Rübartsch's program. The values obtained from these programs are consistent with a relative deviation of 2%. We also analysed the dependence of the dispersion ΔH of the hyperfine magnetic field distribution P(H) as a function of atomic number Z of TM. Some our results have been published, but now we present a full set of our results concerning metallic glasses of the type Fe-TM-B investigated by means of Mössbauer spectroscopy method.

Mössbauer study of disordered, quenched Pd80Co20.

We report M\"ossbauer source experiments on disordered $^{57}\mathrm{CoPd}_{80}$${\mathrm{Co}}_{20}$, and ask if there is any evidence for weak ferromagnetic random anisotropy (RA) near the critical point. In making this search we are encouraged by the fact that Co has an unquenched orbital angular momentum, and that there is evidence of local-moment disalignment in small-angle neutron scattering. Spectra taken over the temperature range 89&lt;T&lt;507 K were well fitted by a continuous magnetic hyperfine field distribution which can be described by a modal field, ${H}_{\mathrm{hf}{}^{m}(\mathrm{T}}$), and a full width at half maximum (FWHM) \ensuremath{\Delta}${H}_{\mathrm{hf}(\mathrm{T}}$). ${H}_{\mathrm{hf}{}^{m}(\mathrm{T}}$) was used to deduce \ensuremath{\beta}=0.38(3) for the range ${10}^{\mathrm{\ensuremath{-}}2}$1-T/${T}_{C}$ 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}1}$. Though insufficiently asymptotic for a strict test of theory, this value is in agreement with predictions for the random-exchange Heisenberg model. \ensuremath{\Delta}${H}_{\mathrm{hf}(\mathrm{T}}$) is found to increase above 320 K, a behavior that can be described via a local-moment mean-field theory which assumes the $^{57}\mathrm{Fe}$ M\"ossbauer site has a 17% FWHM distribution in the exchange constant and a 10% FWHM distribution in ${H}_{\mathrm{hf}(0}$). Neither the deduced critical behavior nor the observed hyperfine-field broadening requires the attribution of RA effects. The only evidence of the possible presence of RA in our experiments is the fact that cold working substantially broadens both ${T}_{C}$ and the hyperfine-field distribution near ${T}_{C}$.

Mössbauer spectrometry study of the hyperfine fields and electronic structure of Fe-Co alloys.

We obtained $^{57}\mathrm{Fe}$ hyperfine-field parameters from M\"ossbauer spectra of Fe-Co alloys at 77 and 295 K. We also obtained the numbers of 3d electrons at Fe atoms by electron-energy-loss spectrometry (EELS). Together with bulk-magnetization data, we deduce how the occupancies of the 3d\ensuremath{\uparrow} and 3d\ensuremath{\downarrow} states at Fe atoms change with Co concentration. Changes in the total numbers of 3d electrons at Fe atoms were found to be small, with the M\"ossbauer data indicating a maximum of about 0.2 electrons at 30 at. % Co, and the EELS data indicating a change of similar magnitude but of opposite sign. From both our isomer-shift and hyperfine-magnetic-field (HMF) data, we deduce a slight reduction in the occupancy of 4s states with Co concentration of ${\mathrm{dn}}_{4s}$/dc=-0.02 electrons, which is principally due to a loss of 4s\ensuremath{\downarrow} electrons. The model employed for the calculation of HMF distributions in terms of conduction- and core-electron polarizations worked well for disordered Fe-Co alloys, and was used to analyze the changes in HMF after the disorder\ensuremath{\rightarrow}order transformation. It showed that these HMF changes upon ordering are primarily due to changes in conduction-electron polarization.