Katarzyna Recko

The crystal and magnetic structures of intermetallic compounds

The powder samples of (x = 4, 5 and 6) alloys have been measured by means of magnetization, Mossbauer effect, x-ray and neutron diffraction techniques in the temperature range 1.5 - 400 K. Both neutron and x-ray diffraction experiments showed that the positions f in all samples are occupied by iron, while the iron atoms in the samples with x = 5 and 6 locate also at j sites. A little f - j disorder exists in . The paper shows a change of the magnetic structure with an increase of iron content. The magnetic moments lie in a basal a - b plane. Iron atoms in alloy order antiferromagnetically. and alloys exhibit in general a ferromagnetic behaviour. However a detailed distribution of magnetic moments among different sites could not be determined unambiguously from the neutron data only. Nevertheless, combining information from neutron and Mossbauer experiments, one can infer that the ordering among iron atoms must be non-collinear. A magnetic ordering among uranium atoms has been found in only. Low-temperature thermal expansion varies nonlinearly with temperature and in all samples is negligible at low temperatures.

Structural and magnetic properties of FeCrAl alloys with DO3-type structure

X-ray, neutron, magnetization and Mossbauer studies in the temperature range 10–300 K are reported for Fe3−xCrxAl system with x < 0.6. The experiments indicate that a single phase having the DO3-type structure is maintained in the range of Cr concentration studied. It was found that Cr atoms occupy preferentially B-sites and the lattice constant decreases with increasing concentration of chromium. The magnetic moment of chromium is small and diminishes the value of neighbouring iron atoms by about 0.1 μB per Cr atom. The magnetic moments of iron at (A, C) and B sites were estimated to be 1.54 (22), 2.58 (22), 1.51 (27) and 2.32 (14) μB for T = 10 and 300 K, respectively. The magnetic moment of iron decreases by 0.37 (10) and 0.26 (6) μB at 10 K and T = 300 K, respectively, if one aluminium atom is found as a nearest neighbour of iron.

Formation of a Partially Oxidized Gold Compound by Electrolytic Oxidation of the Solvoluminescent Gold(I) Trimer, Au3(MeN═COMe)3

The trinuclear complex, Au(3)(MeN=COMe)(3), which displays a number of remarkable properties including solvoluminescence, has been found to undergo electrochemical oxidation with the deposition of long, thin needles on the electrode surface. The electro-deposition process has been studied by cyclic voltammetry, chronoamperometry, and quartz crystal microbalance techniques. The composition of the electrically conducting needles has been determined to be [Au(3)(MeN=COMe)(3)](ClO(4))(0.34) by two complementary methods. The related complex Au(3)(PhCH(2)N=COMe)(3) underwent oxidation at a significantly more positive potential and did not produce a deposit on the electrode surface.

Electric and Magnetic Properties of bcc Fe Based Multicomponent Alloys

The electrical and magnetic properties of a bcc Fe 1- x A x , system with the average atom formed by A = (Al, Si, V, Cr) are presented. Compositions were chosen to obtain alloys of simple structure with control parameter ( x ) covering some important Heusler alloys. Systematic changes in the residual resistivity, magnetic moments, and electronic structure with concentration x are observed. The so-called parallel-resistivity formula ρ -1 =ρ ideal -1 +ρ sat -1 was used for quantitative characterization of the concentrated alloys, where ρ ideal denotes a contribution resulting from different mechanisms of scattering and ρ sat represents a shunt resistivity. At small concentrations x , the main contribution comes from structural disorder. It is shown that the density of states at the Fermi level is substantially reduced at larger x in agreement with results of electronic structure calculations.

Determination of hyperfine fields and atomic ordering in NiMnFeGe exhibiting martensitic transformation

Abstract The hyperfine fields and atomic ordering in Ni1−xFexMnGe (x = 0.1, 0.2, 0.3) alloys were investigated using X-ray diffraction and Mössbauer spectroscopy at room temperature. The X-ray diffraction measurements show that the samples with x = 0.2, 0.3 crystallized in the hexagonal Ni2In-type of structure, whereas in the sample with x = 0.1, the coexistence of two phases, Ni2In- and orthorhombic TiNiSi-type of structures, were found. The Mössbauer spectra measured with x = 0.2, 0.3 show three doublets with different values of isomer shift (IS) and quadrupole splitting (QS) related to three different local surroundings of Fe atoms in the hexagonal Ni2In-type structure. It was shown that Fe atoms in the hexagonal Ni2In-type structure of as-cast Ni1−xFexMnGe alloys are preferentially located in Ni sites and small amount of Fe is located in Mn and probably in Ge sites. The spectrum for x = 0.1 shows the doublets in the central part of spectrum and a broad sextet. The doublets originate from the Fe atoms in the paramagnetic state of hexagonal Ni2In-type structure, whereas the sextet results from the Fe atoms in orthorhombic TiNiSi-type structure.

The crystal and magnetic structures of UFexAl1 2−x alloys

Abstract Powdered samples of UFe x Al 1 2− x ( x = 4, 5 and 6) systems have been measured by means of magnetization, Mossbauer effect, X-ray and neutron diffraction techniques in the temperature range 1.5–400 K. The f-sites in all samples are occupied by iron. Excess iron atoms in samples with x = 5 and 6 are located at j-sites only. The ordering of iron in UFe 4 Al 8 is antiferromagnetic with the iron moment perpendicular to the c -axis. No magnetic moment is seen on U atoms down to 1.5 K. The samples UFe 5 Al 7 and UFe 6 Al 6 exhibit in general a ferromagnetic behaviour. An ordered magnetic moment in the U sublattice is seen in UFe 5 Al 7 only. The Mossbauer spectra suggest that iron magnetic moments at j- and f-sites are only slightly different.