Magnetism in Iron-Zirconium Systems

The discrete variational method is used to solve the Khon-Sham equation in the spin-polarized local density approximation for Fe-Zr and Fe-Zr-H clusters, representing iron-zirconium and hydrogenated iron-zirconium alloys. The local  magnetic moment and hyperfine field at the Fe site were found to decrease, whereas the contact charge density and occupation number were found to increase with Zr contents. The Zr site in clusters with high Fe contents acquires a negative magnetic moment. When H is trapped at an interstitial site next-neighboring an Fe atom, the magnetic moment and hyperfine field are enhanced, while the contact charge density is reduced. ‘The opposite occurs when H occupies a neighboring interstitial site to Fe. For Zr atoms the local magnetic moment is found to become less negative with H at the neighboring position. We conclude from this calculation that H is trapped in Fe-Zr systems at positions which are nearest to Zr and next-nearest to Fe atoms

On the synthesis and cation distribution of aluminum-substituted spinel-related lithium ferrite

Spinel-related Al-substituted Li0.5Fe2.5O4 has been synthesized by sintering a mixture of Al-substituted corundum-related alpha-Fe2O3 and Li2CO3 at 700 degreesC which is ca. 450-500 degreesC lower than the temperatures normally used to prepare the material by conventional ceramic methods. The cation distribution in the material was investigated with X-ray diffraction, Mossbauer spectroscopy and magnetic measurements. Rietveld refinement of the X-ray diffraction data shows the Al3+ ions to substitute for both Fe3+ and Li+ ions on octahedral B-sites while the displaced Li+ ions substitute for Fe3+ ones at tetrahedral A-sites. This structural model is consistent with Mossbauer and magnetic data

Synthesis and cation distribution of copper-substituted spinel-related lithium ferrite

Single-phased Cu2+-substituted spinel-related Li0.5Fe2.5O4 was synthesized by sintering a mixture of Cu2+-substituted corundumrelated alpha-Fe2O3 and Li2CO3 at 700 degrees C which is similar to 325-400 degrees C lower than the temperature at which the material is prepared by the conventional ceramic methods. X-ray powder diffraction, X-ray photoelectron spectroscopy, Mossbauer spectroscopy and magnetic measurements were used to characterize the material. In contrast to high-temperature synthetic routes, the present one leads to a Cu+ and Fe2+-cation free material, thereby optimizing its technological value. Rietveld refinement of the XRD data favors a structural model in which Cu2+ substitutes for both Fe3+ and Li+ at the octahedral sites. Mossbauer and magnetic data are consistent with this model if spin thermal reversal and/or spin canting are taken into account for the later

The formation of lithiated Ti-doped alpha-Fe2O3 nanocrystalline particles by mechanical milling of Ti-doped lithium spinel ferrite

The milling of spinel-related Ti-doped Li0.5Fe2.5O4 for different times is studied with XRD, Mossbauer spectroscopy and magnetic measurements. Milling converts the material to Li-Ti-doped alpha-Fe2O3 nanocrystalline particles via an intermediate gamma-LiFeO2-related phase. The role played by the dopant Ti-ion in the process is emphasized

Cation Distribution in Natural Chromites from Oman

Two specimens or natural chromite from the Oman ophiolite were studied using Mossbauer Spectroscopy (MS), X-ray Diffraction (XRD). and Scanning Electron Microscopy (SEM). The diffraction patterns obtained at room temperature showed that the two specimens have a face-centered cubic spinal structure. Their Mossbauer spectra at 295 K. 160 K and 78 K have been fitted to three doublets. assigned to two Fe 2+ at the tetrahedral (A1+,A2) sites and one Fe1+ at the octahedral (B) site. The ferrous-ferric ratio obtained from the Mossbauer analysis together with the atomic concentration derived from the microprobe data are used to derive the chemical formulae for the two specimens. The data also supports also supports  a model of ordered caution distribution in the specimens examined