Room Temperature 57Fe Research Articles

Mössbauer effect studies of amorphous AlYNiFe alloys

Amorphous AlYNi alloys, prepared by rapid solidification from the melt, have shown a unique combination of low density and high tensile strength. In the present work amorphous alloys of the composition Al 87Y 8Ni 5− x Fe x (2≤ x≤5) have been studied using room temperature 57Fe Mössbauer effect spectroscopy. These alloys show a mean quadrupole splitting which increases slightly with increasing Fe content. The mean isomer shift remains essentially constant as a function of x. All spectra are very nearly symmetric, indicating a weak correlation between the isomer shift and quadrupole splitting. The mean isomer shift is approximately +0.17 mm/s relative to α-Fe and is consistent with Fe probe atoms in a close-packed Al environment.

High-temperature superconductivity in Y 1− zCa zSr 2Cu 2.5Fe 0.5O 6+ x

We report bulk superconductivity with a maximum critical temperature T c of 20 K in single-phase Y 1− z Ca z Sr 2Cu 2.5Fe 0.5O 6+ x (0.05≤ z≤0.18) synthesized under near ambient oxygen pressure. Materials were characterized by X-ray powder diffraction, iodometric titration, magnetic susceptibility, room-temperature 57Fe Mössbauer absorption spectroscopy, and transport measurements. With increasing z, the oxidation state of the Fe-Cu-O array remains essentially constant. Five-fold coordinated Fe in the Cu(1)O x planes appear to be intermediate-spin Fe 3+, all others are present as high-spin Fe 3+. The concentration of Fe 3+ ions in the Cu(2)O 2 sheets increases gradually with increasing z. We interpret the development of a broad maximum versus z near z=0.12 in T c and the Meissner fraction V f to be due to an increasing transfer of holes from the reservoir in the Cu(1)O x planes to the Cu(2)O 2 sheets as the Coulomb repulsion of the positively charged Y 1− z Ca z plane is reduced.

57Fe Mössbauer-effect studies of quadrupole splitting distributions in icosahedral Al-TM-Fe quasicrystals

Room temperature57Fe Mossbauer effect spectra of several Al-TM-Fe icosahedral quasicrystals are reported. Results of fits to discrete sites and to various distributions of quadrupole splittings are presented. Mean isomer shifts,\(\overline \delta \), and quadrupole splittings, Δ, are shown to be insensitive to the fitting procedure used. Trends in\(\overline \delta \) and\(\overline \Delta \) for the icosahedral phase may be indicative of a Hume-Rothery stabilization mechanism.

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.

Magnetic properties and Mössbauer effect in R5Fe 18B 18 ( R1+ϵFe 4B 4)

Samples whose dominant phase is R 5Fe 18B 18 ( R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Lu) were prepared by arc melting and vacuum annealing. Low temperature differential susceptibility measurements on Nd 5Fe 18B 18 indicate a ferromagnetic transition at T ≈ 14K and perhaps a second magnetic transition at T ≈ 7K whose nature is not yet clear. Magnetic transitions were also observed in materials with R = Pr, Sm, Gd, Dy, Ho. Room temperature 57Fe Mössbauer measurements showed all samples to be paramagnetic; the quadrupole splitting and isomer shift were determined. Low temperature Mössbauer measurements indicate no magnetic ordering of Fe down to 1.5 K.

Electrostatic hyperfine interactions in Y(Fe, Al)2

Room temperature57Fe Mossbauer and X-ray diffraction measurements are reported for Y(FexAl1−x)2, 0.1⩽x 0.9. For x⩽0.65 broadened and on the Al-rich side structurized Bragg-peaks are observed. The asymmetry of the quadrupole split Mossbauer spectra depends on x. Whereas two different slopes are obtaind for the concentration dependence of the mean quadrupole splitting on the Al- and the Fe-rich side, the isomer shift exhibits a smooth dependence on x, which can be correlated to the change in volume caused by the Al substitution.

Variability of atomic order and magnetic moments distribution near Fe3Al

Atomic order and magnetic interactions of the Fe-Al alloys near the Fe3Al stoichiometry vary strongly among the A2, B2 and DO3 types of order due to the composition and heat treatment. The type and degree of atomic order of alloys with ca. 20, 24 and 26 at. % Al and various thermal history were gained from the room temperature57Fe Mossbauer spectra. From the calculated magnetic moments distributions, the average moments were inferred and compared with the measured magnetic polarizations. Structural causes of the magnetization variations were drawn.

Magnetic and Mössbauer investigation of REFe4B (RE=Er, Tm, Lu) compounds (abstract)

Magnetic and Mössbauer studies have been carried out on a series of ternary borides REFe4B(RE=Er, Tm, Lu) crystallizing in hexagonal CeCo4B-type structure1. These compounds are found to be magnetically ordered at room temperature. Magnetization studies in the temperature range 5–300 K reveal the presence of compensation temperatures in Er and Tm compounds indicative of antiferromagnetic coupling between the rare-earth and Fe moments. Room-temperature 57Fe Mössbauer studies yield values of hyperfine fields of 246, and 185 kOe in LuFe4B. The 166Er Mössbauer studies give an almost free ion hyperfine field at the Er site, indicating that exchange interaction in ErFe4B is much stronger than the crystal field effects.

57Fe and 166Er Mössbauer and magnetic studies of RFe 4B (R = Er, Tm, Lu) compounds

Magnetic and Mössbauer studies have been carried out on a series of ternary borides RFe 4B (R = Er, Tm, Lu) which have the hexagonal CeCo 4B type structure. These compounds are found to be magnetically ordered at room temperature. Magnetization studies in the temperature range from 5 to 300 K reveal the presence of compensation temperatures in Er and Tm compounds and indicate antiferromagnetic coupling between the rare earth and Fe moments. Room temperature 57Fe Mössbauer studies yield values of hyperfine fields at the two Fe sites as 246 and 185 kOe in ErFe 4B and TmFe 4B, and 204 and 145 kOe in LuFe 4B. The 166Er Mössbauer studies give nearly free-ion hyperfine field at the Er sites which indicates that the exchange interaction in ErFe 4B is much stronger than crystal field interaction.

Some physical properties of LaFe 4P 12 type compounds

Several pnictides with the filled skutterudite (LaFe 4P 12 type) structure were investigated by X-ray diffraction, magnetic susceptibility and electrical conductivity measurements and Mössbauer spectroscopy. The structure refinement of CeFe 4P 12 from single crystal X-ray data resulted in a conventional residual value of 0.022 for 11 variable parameters and 317 reflections. LaFe 4P 12 and CeFe 4P 12 are paramagnetic at room temperature. EuFe 4P 12 is a ferromagnet with a Curie temperature of 99 K. CeFe 4P 12 and CeFe 4As 12 are semiconducting. LaFe 4Pn 12 ( Pn = P, As or Sb) and CeFe 4Sb 12 show metallic conductivity. The room temperature 57Fe Mössbauer spectra of LaFe 4P 12, CeFe 4P 12 and EuFe 4P 12 are symmetrical doublets. The isomer shifts are compatible with low spin or metallic Fe. At 1.5 K the 57Fe Mössbauer spectrum of EuFe 4P 12 under an external field shows that Fe does not carry any magnetic moment. 151Eu Mössbauer spectra of EuFe 4P 12 at 4.2 and 300 K show unusual hyperfine parameters.

Ferric/ferrous-iron ratios in bulk rock samples by Mössbauer spectroscopy — The determination of standard rock samples G-2, GA, W-1 and mica-Fe

Room-temperature 57Fe Mössbauer spectra have been recorded for the USGS rock-standards G-2 and W-1; the CRPG standards GA and mica-Fe; and an “in-house” standard, NS. A comparison of the results of ferric/ferrous-Fe ratios by chemical and Mössbauer analysis is presented. The errors involved in each method are assessed. In the low-Fe rocks, chemical analysis appears to considerably over-estimate ferric content although the spread of individual laboratory values tend to a low limit close to the Mössbauer values.

Studies of magnetic ordering in Cu 2FeSnS 4 by Mössbauer spectroscopy

Cu 2FeSnS 4, a tetragonal crystal of space group 142 m, is found by magnetic measurements to undergo an antiferromagnetic transition at 7°K. Mössbauer measurements at the iron and tin sites at 4°K are reported. Analysis of the 57Fe results yields a quadrupole splitting of −2·7 mm/sec and a hyperfine field which is perpendicular to the tetragonal axis and equals to 205 KOe. The sign of the quadrupole splitting is corroborated by room temperature 57Fe Mössbauer spectra in an external field of 28 KOe but found to disagree with a point charge calculation. From the sign of the quadrupole splitting one can deduce the orbital ground state of the Fe 2+ ion to be |3Z 2− r 2) and calculate, the single ion anisotropy. This leads to the prediction that the axis of the sublattice magnetization is perpendicular to the tetragonal axis, a prediction which is verified by the low temperature Mössbauer measurement. The 119Sn spectrum yields an hyperfine field of about 20 KOe. Assuming the chemical and magnetic cell to be equal a magnetic space group of Ip 222 or Ip mm2 follows.

Effects of Atomic Configurational Changes on Hyperfine Interactions in Concentrated Iron-Cobalt Alloys

Room temperature 57Fe Mössbauer spectra were taken on atomically ordered and disordered iron-cobalt samples as a function of composition between 25 and 75 at.% cobalt. The degree of long-range order was determined in selected samples using neutron diffraction. The maximum values of the effective field (He) and isomer shift (I.S.) occur at 25 at.% cobalt where He=−365.5±0.5 kOe and I.S. = +0.037±0.005 mm/sec (relative to pure iron). In the composition range studied increasing the number of cobalt neighbors to an iron atom either by ordering or by increasing the cobalt concentration decreases both I.S. and He. The maximum decrease with ordering of I.S., He, and the line widths occurs at 50 at.% cobalt, where the decrease is about 0.02 mm/sec for I.S. and 10 kOe for He. These results indicate that local atomic configurations play a significant role in the competition between positive and negative contributions to He. The data suggest a positive spin polarization contribution at the nucleus.