Mössbauer study of the '11' iron-based superconductors parent compound Fe(1+x)Te.

(57)Fe Mössbauer spectroscopy was applied to investigate the superconductor parent compound Fe(1+x)Te for x = 0.06, 0.10, 0.14, 0.18 within the temperature range 4.2-300 K. A spin density wave (SDW) within the iron atoms occupying regular tetrahedral sites was observed, with the square root of the mean square amplitude at 4.2 K varying between 9.7 and 15.7 T with increasing x. Three additional magnetic spectral components appeared due to the interstitial iron distributed over available sites between the Fe-Te layers. The excess iron showed hyperfine fields at approximately 16, 21 and 49 T for three respective components at 4.2 K. The component with a large field of 49 T indicated the presence of isolated iron atoms with large localized magnetic moments in interstitial positions. Magnetic ordering of the interstitial iron disappeared in accordance with the fallout of the SDW with increasing temperature.

Calibration of the isomer shift for iodine resonant transitions by ab initio calculations.

The isomer shift calibration constants have been calculated for 57.60 keV in 127I and for 27.72 keV in 129I resonant transitions by density functional theory. The full-potential linearized augmented plane-wave method (FLAPW) was applied in the scalar-relativistic approach. The NaI compound was used to set the origin of the scales in both cases. On the basis of the existing experimental data, the following values for the calibration constants were obtained: alpha = -0.057(2) mm s(-1) au3 for 127I and alpha = +0.164(4) mm s(-1) au3 for 129I. The ratio of the calibration constants of alpha127/alpha129 = -0.35(1) was established. Spectroscopic electric quadrupole moments for the ground state of the above nuclei have been calculated as byproduct. The quadrupole moments Q(g)(127) = -0.764(30) b and Q(g)(129) = -0.731(3) b were obtained for 127I and 129I, respectively. Errors quoted are due to the linear regression fit, and real errors might be as large as about 10% of the quoted absolute value.

Properties and microstructure of the (Fe, Ni)-Cu-(P, Si, B) melt-spun alloys.

The work presents the microstructure characterization of the new (Fe, Ni)-Cu-(P, Si, B) melt-spun glass forming alloys investigated by means of transmission electron microscope. The results are compared with the data obtained by other complementary methods such as XRD and Mössbauer spectroscopy. The phases occurring during the crystallization of the glassy matrix are identified and characterized in terms of a long-range order and a short-range order. The thermal stability of the alloy is characterized by differential scanning calorimetry. The study describes the mechanical and magnetic properties of the new alloys at room temperature as well as characteristics resulting from heating the as-cast melt-spun alloy at elevated temperatures. The changes of the properties of the alloy at elevated temperatures are correlated with the microstructural changes.

Fractal-like behaviour of the BCC/FCC phase separation in the iron-gold alloys.

Iron-gold alloys with compositions Fe(70)Au(30) and Fe(50)Au(50) were prepared by arc melting. The alloys were investigated by means of the high-resolution scanning electron microscopy (SEM-FEG) in the as-cast state and upon annealing in two steps, i.e. at 250 degrees C for 24 h and subsequently at 500 degrees C for 48 h. The alloys were composed of two phases, i.e. a BCC phase rich in iron and a FCC phase rich in gold. The single-phase regions have equivalent diameter of about 50 nm. SEM images show self-similar structure for the spatial distribution of the above phases on scales ranging from about 1 mm till about 100 nm. The roughness of the images has been used to estimate a fractal dimension of the phase mixture. For larger scales of the as-cast samples one finds fractal dimension of about 1.7 for Fe(70)Au(30) composition, i.e. very close to the dimension of typical diffusion limited aggregation (DLA) fractals. For annealed samples, dimension 1.1 was found.

Calibration of the isomer shift for the 77.34 keV transition in 197Au using the full-potential linearized augmented plane-wave method.

The isomer shift calibration constant has been calculated for the 77.34 keV Mossbauer transition connecting the ground state of the (197)Au nucleus with the first excited state of this nucleus. The full-potential linearized augmented plane-wave method was used in the fully relativistic approach, albeit without taking into account the spin-orbit coupling. The final assignment of the calibration constant was based on calculations performed for AuCN, AuCl(3), AuBr(3), KAuCl(4), KAuBr(4), and metallic gold. It is found that the calibration constant takes on the following value alpha = +0.0665(4) mm s(-1) a.u.(3). The error quoted is due to the linear regression fit, and the real error might be as large as 10%. The spectroscopic electric quadrupole moment for the ground state of the (197)Au nucleus was calculated as the by-product. It was found that this moment equals Q(g) = +0.566(1)b in fair agreement with the accepted value based on the muonic hyperfine spectroscopy results. The error quoted is again due to the linear regression fit and the real error might be as large as 10%. The final assignment of the value for the quadrupole moment is based on the calculations for the following compounds: AuCl, AuBr, AuI, AuCN, and AuMn(2). Results for the magnetically ordered Au(2)Mn were applied to determine the sign of the quadrupole moment.