Average Isomer Shift Research Articles

Investigation of Zn-Fe alloy coating

The solubility of Zn atoms in α-Fe is increased by electrodeposition. The lattice constant of electrodeposited FeZn alloys increases with increasing Zn concentration. The average internal magnetic field and isomer shift of electrodeposited FeZn alloys are strongly correlated with Zn concentration. For FeZn alloys with Zn concentrations > 52 at.%, the Mössbauer spectra consist of an α-phase and a ZnFe intermediate phase.

Magnetic hyperfine field distributions of amorphous FeB alloy particles and ribbons

Amorphous Fe 1− x B x alloy particles, prepared by a chemical reduction method, and ribbons, produced by the melt-spin method, have been investigated by Mössbauer spectroscopy. The average magnetic hyperfine fields and isomer shifts for ribbons and particles are found to resemble each other, but the hyperfine field distributions for the particles are significantly wider than for the ribbons. This indicates that the two types of alloys have slightly different amorphous structures.

Mössbauer study of Gd 2Fe 17C 2.0 compound by the melt quenching

Carbide of composition Gd 2Fe 17C x compound with higher carbon concentration x=2 was successfully prepared by the melt quenching. 57Fe Mössbauer spectra of the carbides ( x=0,1,2) were measured at room temperature, the results show that the changing tendency of average hyperfine field and isomer shift is consistent with that of the carbides with x<1.5. The effects of the interstitial carbon atoms in the Gd 2Fe 17 compound on the hyperfine parameters were discussed.

Studies of Mossbauer spectra for nitrides RTiFe11Nx (R=Y, Nd, Sm, Gd and Er)

Magnetic properties and 57Fe Mossbauer spectra for the nitrides, RTiFe11Nx, and for their parents RTiFe11 (R=Y, Nd, Sm, Gd and Er) have been studied. The Curie temperatures of RTiFe11Nx increase by 135-200 degrees C over those for RTiFe11. The maximum Curie temperature is 745 K for GdTiFe11Nx. The Fe atomic moments at room temperature are 1.84 mu B and 1.52 mu B for YTiFe11Nx and YTiFe11, respectively. Mossbauer spectra of the nitrides are fitted by using seven sets of subspectra, needed because the N atoms affect the hyperfine parameters. As compared to RTiFe11, the average hyperfine field increases by 5-9 T and the average isomer shift by 0.10-0.18 mm s-1 for RTiFe11Nx. For most of the RTiFe11 series and their nitrides, the average hyperfine fields have a linear relationship with (gR-1) JR which can be understood with the RKKY theory. The core electron polarization field, Bcp, 4s electron polarization field, B4s, and transfer field, Bmp, have been analysed and compared for the Y compound. The N atoms bring about an increase in magnitude of Bcp and Bmp and a decrease in magnitude of B4s, which leads to an average increase of about 9 T in magnitude for the hyperfine field of YTiFe11Nx as compared to YTiFe11. The proportionality coefficient between the average hyperfine field and the Fe moment for YTiFe11Nx deviates far from the normal value of 15T mu B-1. This is attributed to a very large increase in the total conduction-electron polarization field.

A Mössbauer effect study of the microscopic magnetic properties of Nd2Fe17 and Nd2Fe17N2.6

The Mössbauer spectra of Nd2Fe17 and Nd2Fe17N2.6 have been measured at various temperatures between 78 and 295 K and analyzed with a model that is based on the Wigner–Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron-diffraction measurements or band-structure calculations. Upon nitrogenation of Nd2Fe17, the weighted average isomer shift increases from 0.060 to 0.164 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed in their Wigner–Seitz cell volumes and the presence of a nitrogen near neighbor for two of the sites. Upon nitrogenation of Nd2Fe17, the weighted average hyperfine field increases from 292.3 to 333.8 kOe. However, the increases on the 6c and 18f sites are much smaller than those observed on the 9d and 18h sites; changes which are in agreement with calculated changes in the magnetic moments upon nitrogenation of Nd2Fe17, Gd2Fe17, and Y2Fe17. The temperature dependence of the isomer shifts indicates an increase in covalency upon the formation of the nitride.

A comparison of the Mössbauer effect spectra of R 2Fe 14B and R 2Fe 14C

The Mössbauer spectra of R 2Fe 14B, where R is La, Tb, Dy, Ho and Lu, have been measured at 295 K and the Mössbauer spectra of R 2Fe 14C, where R is Nd, Ho and Gd, have been measured at various temperatures between 85 and 295 K. All of the resulting spectra have been successfully analyzed with the same model used earlier to fit the spectra of various related compounds. The results indicate that the weighted average hyperfine field increases uniformly from La to Gd and decreases uniformly from Gd to Lu in R 2Fe 14B, as was found earlier for R 2Fe 14C. The weighted average isomer shift decreases by 0.04 mm/s in going from La 2Fe 14B to Lu 2Fe 14B, because of a decrease in the unit cell volume and an increase of the number of electrons in the unit cell, a decrease which corresponds to a 13.5% increase in the electron density. The use of the same model for both the Nd, Gd, Tb, Dy, Ho and Lu borides and carbides permits a detailed comparison of the Mössbauer hyperfine parameters in the two series of compounds. There is a linear correlation of the hyperfine fields at each of the sites in these two series of compounds, indicating that the replacement of boron by carbon has a long-range effect on the magnetic exchange within these materials. There is a correlation of the isomer shifts of the 8j 1, 8j 2 and 16k 2 sites in the two series of compounds. In contrast the isomer shift of the 16k 1 site show the chemical influence of replacing boron by carbon. With the expected exception of the 4c site there is a correlation between the quadrupole interactions in the two series of compounds. The Nd 2Fe 14B and Nd 2Fe 14C compounds have relatively low effective Mössbauer temperatures as compared to the borides and carbides with the heavier rare-earth elements.

Local atomic environment parameters and magnetic properties of disordered crystalline and amorphous iron-silicon alloys

The dependences of the specific saturation magnetization sigma (C), magnetic ordering temperature TC(C), average hyperfine field H(C) and average isomer shift delta (C) on Si concentration are measured in crystalline Fe-Si alloys disordered by mechanical crushing. It is shown that topological disordering does not determine the magnetic properties. The peculiarities found are explained in terms of the local atomic structure parameters depending on the number of Si nearest neighbours of an Fe atom.

Mössbauer study of magnetic properties formation in disordered Fe-Al alloys

For by mechanical treatment disordered Fe-Al alloys in the concentration range of Al from 0 to 60 at% the average hyperfine field, H , and isomer shift, η , values, the magnetic ordering temperatures T c and the average magnetic moment m per Fe atom were measured in Mössbauer and magnetometric studies. An explanation for the features of the concentration dependence H ( x) is proposed in terms of the local hyperfine field H K dependence obtained experimentally, and the local atomic environments probabilities. Proceeding from the data concerning the behaviour of the average and local hyperfine fields and the local atomic configurations, a model for the local magnetic moments m K on the Fe atom, which describes the form of the average magnetic moment m as a function of Al content, was constructed.

Magnetic and57Fe Mössbauer studies of intermetallic compounds R2 (Fe1−x−y Ni x Co y )17 (R=Y,Gd,Tb,x=0,0.10, 0.20,y=0,0.05, 0.10)

Mossbauer studies of R2(Fe1−x−yNixCoy)17 showed that the transferred hyperfine field at Fe nuclei due to magnetic rare earth (R) atoms is about one Tesla. Magnetic moments of the R atoms were determined from magnetic measurements as μTb=8.52μB, μGd=6.22μB. The mixed substitution of Ni and Co for Fe leads to an increase of the ordering temperature. A slight preference occupancy for Fe was observed involving the dumbbell shaped f or c site. The substitution effects of Ni and Co on the hyperfine field of f or c site, the average hyperfine field and the average isomer shift were also discussed.

Mössbauer studies of YTi(Fe1−xMx)11 (M=Co and Ni)

57Fe Mössbauer spectra of YTi(Fe1−xMx)11 (M=Co and Ni) have been studied. The average isomer shifts increase monotonically. The average quadrupole splittings have a sudden change for YTi(Fe1−xCox)11 between x=0.4 and 0.6. It appears that a spin reorientation occurs over this composition range. Both hyperfine fields for the three sites and the average field increase at first, and then decrease with increasing Co or Ni concentration. The maximum of the average hyperfine field is 27.7 T at x=0.6 for YTi(Fe1−xCox)11 and 24.1 T at about x=0.2 for YTi(Fe1−xNix)11. The average moments of Co and Ni atoms are 1.3(1)μB and 0.6(1)μB, respectively, obtained from the formula μ = (1 − x)μFe + xμT.

Fe-B-Si系アモルファス合金の不可逆的構造緩和過程

Irreversible structural relaxation processes have been investigated for Fe75B10Si15, Fe78B7Si15 and Fe79B10Si11 amorphous alloys by electrical resistivity measurements and Mössbauer spectroscopy.The electrical resistivity of as-quenched alloys decreased irreversibly with isothermal annealing. Such resistivity changes are mainly associated with decrease of free volume introduced by quenching from the melt. The irreversible decrease of resistivity was reproduced well using the free-volume-Ziman model which was based on the Ziman theory of resistivity and the free-wolume model for viscous flow. The activation energy for annihilation of free volume was evaluated to be 222 kJ/mol (Fe75B10Si15) and 154 kJ/mol (Fe78B7Si15, Fe79B10Si11) from resistivity changes. On the other hand, a significant difference in the annealing behavior of the average isomer shift and internal magnetic field with time between Fe75B10Si15 and Fe78B7Si15 amorphous alloys was observed. This indicates that the local structural change in relaxation process differs much in both amorphous alloys. Such compositional dependence of activation energy and Mössbauer parameters was explained well by the structural model proposed by Dubois et al.

A Mössbauer effect study of the Re2Fe14B magnets, where RE is Y, Pr, Nd, and Gd

The Mossbauer spectra of Pr2Fe14B and Gd2Fe14B have been measured from 85 to 295 K and fit with a second order approximation in which the angle, ϕ, between the principal axis of the electric field gradient and the easy-axis of magnetization has been fixed by the positions of the near-neighbor rare-earth atoms. The coordination environment for each of the six iron sites in these materials has been determined from the Wigner-Seitz cell and used in the spectral analysis. The hyperfine parameters resulting from the above fit are in agreement with the structural and electronic properties of these compounds and also agree well with those determined in our earlier studies of Nd2Fe14B and Y2Fe14B. The magnetic hyperfine fields for the different sites are similar in the Y, Pr, and Nd compounds but are, as expected, higher in the Gd compound because of the much higher spin-multiplicity associated with Gd. The hyperfine fields on the 8j 1 and 4c sites, which have the most rare-earth near-neighbors show, as expected, the largest variation with rare-earth atom. The quadrupole interactions are constant with temperature and the absolute value of the quadrupole interactions on the 8j 2 and 4e site are found to be the largest, as is consistent with the highly distorted environment of these sites With the possible exception of the 4c site, the quadrupole interaction shows little variation with rare-earth atom. The isomer shift for each site in each compound varies linearly with temperature, as expected, for the second-order Doppler shift and gives effective Mossbauer masses between 62 and 67 g/mole. The weighted average isomer shift is similar in each of these compounds, but the isomer shifts associated with some of the specific sites in Gd2Fe14B are rather different than in the Y, Pr, and Nd compounds.

Mössbauer study of Fe-B alloys containing Nd additives

The influence of a few percent neodynium additives to Fe-B alloy on the hyperfine parameters was investigated. It was found that Nd decreases the hyperfine field of amorphous Fe-B alloys. The samples annealed at temperatures between 600°C and 700°C contain α-Fe and Fe3B phases. The average hyperfine field of Fe3B phase increases with increasing Nd content and decreases with increasing annealing temperature. The average isomer shift of Fe3B phase decreases with increasing Nd content. The experimental data show that the change of hyperfine parameters of the Fe3B phase in the studied alloys is due to Nd atom.

Mössbauer study of Fe-substituted Co-Zr and Cu-Zr metallic glasses

The structure of pseudobinary Co-Zr and Cu-Zr metallic glasses, where Co and Cu were substituted by Fe, was studied by means of 57Fe-Mössbauer spectroscopy. The resulting spectra can be divided into two different classes: (1) For Zr concentrations larger than 67 at. %, the structure of the glass, as derived from Mössbauer spectroscopy, is nearly independent from a substitution, leading to only small changes of the average isomer shifts and quadrupole splittings. These small variations of hyperfine parameters can be ascribed to charge transfer effects. (2) For lower Zr contents, pronounced systematic changes of hyperfine parameters occur upon Co or Cu substitution. Beyond changes of the average hyperfine values, the corresponding quadrupole-splitting distributions become dependent on the degree of substitution, i.e., there is a concentration dependent splitting into two peaks. For the amorphous binary Zr-Fe system, these two peaks have been connected to two amorphous phases with concentrations near Zr2Fe and ZrFe2. At least for the Fe-doped Cu-Zr metallic glasses it could be demonstrated that Fe does not substitute the Cu sites but rather creates preferred environments.

Mössbauer spectra of tris(diorganothioselenocarbamato)- and tris(diorganodiselenocarbamato)iron(III) complexes

Room temperature 57Fe Mössbauer spectra of several tris(diorganothioselenocarbamato)- and tris(diorganodiselenocarbamato)iron(III) complexes are reported, along with their room temperature magnetic moments for the solid state. These results are compared to the previously reported diethyl derivatives and to the corresponding monothio- and dithiocarbamates. Each complex exhibited a single, quadrupole-split absorption in its Mössbauer spectrum. Although variations are noted within specific organic substituents, general trends for the average isomer shifts of all ligands are −OSCNR 2 < −S 2CNR 2 ∼ −SSeCNR 2 ∼ −Se 2CNR 2, while the typical order of the quadrupole splittings for a given ligand is −OSCNR 2 < −S 2CNR 2 < −SSeCNR 2 < −Se 2CNR 2. For the same organic substituent, the magnetic moments usually decrease in the order −OSCNR 2 > −S 2CNR 2 > −SSeCNR 2 > −Se 2CNR 2. It is noteworthy that higher quadrupole splittings are observed for the symmetric diselenocarbamate iron(III) complexes than for the corresponding thioselenocarbamates.

A Moessbauer analysis of the low-potential iron-sulfur center in photosystem I: spectroscopic evidence that FX is a iron-sulfur [4Fe-4S] cluster

We report the results of a Mössbauer study of the low-potential iron-sulfur cluster FX in the Photosystem I core protein of Synechococcus 6301. The Mössbauer spectrum of FX in the oxidized state shows an isomer shift of 0.42 mm/s, which is in good agreement with the 0.43 mm/s isomer shift found in [4Fe-4S] proteins but not with the isomer shift of 0.26 mm/s found in [2Fe-2S] proteins. In the reduced state the spectrum is asymmetrically broadened at 80 K, indicating the presence of two very closely spaced doublets with an average isomer shift of 0.55 mm/s, which is also in agreement with [4Fe-4S] proteins. At 4.2 K, the spectrum exhibits broadening and magnetic splitting similar to what is observed for [4Fe-4S] proteins and quite unlike [2Fe-2S] proteins. Given the assumption that the iron atoms of FX are tetrahedrally coordinated with sulfur ligands, the data strongly support the assignment of FX as a [4Fe-4S] cluster.

Tin Mössbauer spectroscopy of tin-rich iridium-tin alloys

Ir5Sn7, Ir3Sn7 and newly obtained IrSn4 /4/ exhibit complex Mossbauer spectra. The positions of the individual lines range from 0.82 to 3.0 mm/s and the average isomer shift\(\overline {IS} \) derived for each compound of Sn atomic percentage x follows the relationship:\(\overline {IS} = 0.60 + 0.0194 x\). Rather large quadrupole splittings are obtained. The f factors are about 0.20 at 295 K and 0.37 at 78 K, from which Debye temperatures of 200 to 300 K have been calculated.

Influence of vanadium on the 57Fe-site spin and charge densities in cobalt-vanadium alloys.

The influence of substitutional vanadium on spin and charge densities has been studied for a series of hcp ${\mathrm{Co}}_{100\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{V}}_{\mathrm{x}}$ alloys with x\ensuremath{\le}12.5, using $^{57}\mathrm{site}$ M\ossbauer spectroscopy. It has been shown that one V atom residing in the first-neighbor shell reduces the $^{57}\mathrm{site}$ hyperfine field by \ensuremath{\Delta}${H}_{1}$=38.4 kOe and the isomer shift by \ensuremath{\Delta}${I}_{1}$=0.020 mm/s which means an increase of the charge density by \ensuremath{\Delta}${N}_{1}^{s}$=0.01 s electrons. The influence of one V atom as a second-nearest neighbor is similar in sign but three times smaller in magnitude. The maximum change of the charge density (i.e., that due to three V atoms per unit cell) which can be evaluated from the correlation between the average hyperfine field and the average isomer shift amounts to \ensuremath{\eta}=0.03\char21{}0.05 s electrons. The results are compared with those obtained for the bcc Fe-V system.

Platinum-induced changes in the electronic structure of iron.

By means of the M\"ossbauer-effect spectroscopy and the nuclear magnetic resonance the influence of substitutional platinum on spin- and charge-density changes in a metallic iron is studied in order to further test the Miedema--van der Woude model which for a change of the charge-density caused by one Pt atom in a unit cell predicts a value of \ensuremath{\eta}=-0.34(4). From linear correlations between the average hyperfine field H\ifmmode\bar\else\textasciimacron\fi{} and the average isomer shift, as well as between H\ifmmode\bar\else\textasciimacron\fi{} and the concentration of platinum, a value of \ensuremath{\eta}=-0.21(1) is found. The influence of Pt atoms turns out to be extremely long ranged, as the impurities residing at least up to the thirteenth coordination shell must be included in order to properly describe the observed effects.

Rhenium-induced changes in the electronic structure of iron

Influence of substitutional rhenium on spin- and charge-density changes in metallic iron is studied by means of the 57Fe Mössbauer spectroscopy and the nuclear magnetic resonance in Fe 100− x Re x alloys with x up to 10. From the linear correlations between the average hf field, H̄ and the corresponding average isomer shift, Ī as well as between H̄ and the average number of Re atoms within the first two neighbour shells of 57Fe nuclei, a change of spin(charge)-density at Fe nucleus due to one Re atom per unit cell, η = -0.019(6) is estimated. The result agrees well with the value expected from the Miedema-Van der Woude model.