E. Wu

Structural study of the rare-earth transition-metal intermetallic compound Nd3Ni29Si4B10

The novel quaternary rare-earth transition-metal intermetallic compound Nd3Ni29Si4B10 of space group P4/nmm (No. 129) has been synthesised and its structure determined. The crystal structure has been investigated by scanning electron microscopy, X-ray and neutron powder diffraction measurements. Rietveld refinements of the powder X-ray and neutron diffraction patterns reveal a tetragonal structure of lattice parameters a=b=11.2327(7) A, c=7.8754(3) A with two formula units of Nd3Ni29Si4B10 per unit cell. The structure contains two rare-earth crystallographic sites of high symmetry, four B sites, seven transition metal sites and one Si site. The Ni atoms at the 2c 4 mm crystallographic site have a quasi-spherical polyhedral coordination.

A Mössbauer effect study of barium ferrite ball-milled in air

The effects of dry-milling BaFe12O19 in air for periods of 190, 360, 590, 690 and 1000 h have been investigated by X-ray diffraction and Mössbauer effect measurements. The sizes of the BaFe12O19 particles decrease on milling, as expected, although a partial decomposition of BaFe12O19 to α-Fe2O3 is found to take place on extended milling (1000 h). The room temperature Mössbauer spectra are consistent with superparamagnetic relaxation associated with the fine BaFe12O19 and α-Fe2O3 particles. The X-ray diffraction patterns of all the milled samples exhibit features indicative of a disordered structural state, consistent with the nanoscale particles and a nanostructured state.

A Mössbauer effect study of ball-milled strontium ferrite

Abstract The effects of milling SrFe 12 O 19 in air and vacuum for 800 h have been investigated by X-ray diffraction and Mossbauer effect spectroscopy measurements. Different levels of structural disorder along with partial decomposition of SrFe 12 O 19 to nanocrystalline grains of haematite, α-Fe 2 O 3 , and magnetite, Fe 3 O 4 , are obtained for the air and vacuum milling. Superparamagnetic relaxation effects due to the fine particles produced on milling are observed for a significant fraction ( ∼ 10% air milled, ∼ 30% vacuum milled) of the milled samples.

Magnetization study of rare-earth intermetallic compounds R3Co29Si4B10

YBa2Cu3Ox (YBCO) thin films grown on different substrates with and/or without Eu2CuO4 (ECO) buffer layer were investigated by X-ray wide angle diffraction, reflection, diffuse scattering and topography. The results show that for the yttria stabilized ZrO2 (YSZ) substrate, the presence of an ECO buffer layer improves the crystalline quality of the YBCO film, while a negative effect is observed for the SrTiO3 (STO) substrate. The lateral correlation length for a sample grown on a YSZ substrate with ECO buffer layer is much greater than that grown on an STO substrate. The STO substrate used has mosaic structure

Formation of the quaternary compounds Nd3(T1−xSix)33B10 (T=Co, Ni; 0.115≤x≤0.150)

Abstract A series of quaternary rare-earth transition-metal intermetallic compounds based around the composition Nd 3 T 29 Si 4 B 10 (T=Co, Ni) has been synthesised successfully, although it is found that the compound does not form for T=Fe. The new phase is designated by Nd 3 (T 1− x Si x ) 33 B 10 (0.115≤ x ≤0.150) and has a tetragonal structure with space group P 4/ n m m (No. 129). The Nd 3 Ni 29 Si 4 B 10 compound has close links with the ternary compounds NdNi 9 Si 2 and NdNi 12 B 6 .

Site occupation in57Fe doped NdCo12B6: Mssbauer analysis

The analysis of room temperature and4.2 K Mössbauer spectra of NdCo12B6 doped with57Fe is presented. A clear preference of the57Fe atoms for the 18h sites, of increased number of Co near neighbour atoms compared with the 18g site, is obtained in good agreement with recent studies of related 1:12:6 compounds.

Magnetic behaviour of Nd3Co29Si4B10

Abstract The magnetic behaviour of a novel quaternary rare-earth compound Nd 3 Co 29 Si 4 B 10 has been investigated by AC magnetic susceptibility and 57 Fe Mossbauer effect spectroscopy measurements. The Nd 3 Co 29 Si 4 B 10 compound exhibits a magnetic transition around T c1 ≈ 200 K with a second magnetic transition occurring around T c2 ≈ 43 K. Addition of ≈ 0.5 wt% 57 Fe is found to decrease the magnetic ordering temperatures to T c1 ≈ 167 K and T c2 ≈ 38 K. Similar to other Co-rich, light rare-earth compounds, Nd 3 Co 29 Si 4 B 10 is likely to exhibit ferromagnetic ordering below T c1 .

Mössbauer and X-ray studies of an iron meteorite sample

Detailed analysis of the room temperature Mössbauer spectrum of an Fe-Ni (≈ 91.9% Fe, 7.5% Ni) meteorite from the Henbury crater region of northern Australia shows that it behaves identically to an Fe-Ni alloy. The enhanced resonance absorption is due to thickness effects, with the line broadening reflecting a range of atomic environments. The isotope ratio56Fe/57Fe for the meteorite agrees with the earth bound values.

Crystal structure of a quaternary Nd–Ni–Si–B compound-refinement of synchrotron radiation data

Abstract High-resolution synchrotron-radiation powder data have been obtained for a new quaternary Nd–Ni–B–Si compound with the nominal composition of NdNi 8 SiB 3 . The data were collected on a (573 mm radius) cylindrical cassette diffractometer using imaging plates. The crystal structure of the new compound has been determined and refined by Rietveld analysis. The initial structural model and space group for the refinement is based on insight derived from earlier Mossbauer and TEM analyses. Refinement of the powder data leads to a tetragonal unit-cell with lattice parameters a =11.2260(2) A and c =7.8731(2) A in the space group P4/nmm. The refined compound is found to have a composition of NdNi 9.7 Si 1.3 B ∼4 . The atomic coordinates for the Nd, Ni and Si atoms have been determined. Small amounts of the impurity phases, NdNi 5 and Nd 3 Ni 13 B 2 , have also been determined and refined in the analysis.

Mössbauer effect study of57Fe-doped LaCo12B6

Mössbauer spectra of LaCo12B6 doped with57Fe have been obtained at various temperatures between 4.2 and 293 K. The observed splitting of the subspectrum associated with the 18h site belowTC indicates that the Co sublattice of LaCo2B6 remains ordered in the crystallographic basal plane, with no discernible change in magnetic ordering direction belowTC, contrary to the recent suggestion of a change in magnetic states based on NMR data.