Mössbauer studies on Al−Co ferrites

Mössbauer spectroscopy studies have been performed on the spinel CoAl_xFe_2?xO₄ (2<-x<-1.7) in the temperature range 77–750 K using either a liquid nitrogen bath cryostat or a furnace. The samples are magnetic at 77 K giving spectra that have magnetic sextets coexisting with a central line which increases in population with the Al-content indicating relaxation effects. The data shows that Al possesses no preference to either tetrahedral or octahedral sites of the ferrite over the whole range of concentration. The Mössbauer hyperfine interaction parameters and magnetic transition temperatures were determined. As expected the hyperfine field and Curie temperature decrease when the Al-content increases.     

Structural characterization and magnetic properties of NiMg3x/2Cr0.9Fe1.1 − x O4

Magnesium-substituted nickel–chrome ferrites have been studied using X-ray diffraction and Mössbauer spectroscopy. A single cubic spinel phase was obtained in the range 0.0?≤?x?≤?0.4. The lattice parameter was found to decrease with the increase of Mg concentration. The Mössbauer spectra measured at 295 and 78 K of all samples showed magnetic patterns interpreted in term of the tetrahedral and octahedral sites occupancies. The magnetic hyperfine field of both sites decrease with the increase of the Mg concentration. The magnetic properties as a function of the Mg concentration have been explained on the basis of the cation distribution among the two crystallographic sites driven from the Mössbauer measurements.     

Effect of vanadium neighbors on the hyperfine properties of iron–vanadium alloys

The electronic and magnetic structures of Fe–V alloys are calculated using the discrete-variational and full-potential linearized-augmented-plane wave methods. The derived hyperfine properties at Fe sites are studied against the number of Fe atoms in the neighbouring shells. As expected the magnetic hyperfine field depends strongly on the number of Fe atoms in the first and second shells of neighbours while its dependence on the variation of atoms in the third shell is weak. The calculated distribution of the magnetic hyperfine fields at the Fe sites, are compared to the experimental data of Krause et al. (Phys Rev B 61:6196–6204, 2000). The contact charge densities and the magnetic moments are also calculated. It was found that the contact charge density increases with increasing V contents and this leads to negative isomer shift on addition of V.     

Hyperfine field and isomer shift in ferromagnetic Fe−Cr alloys

The valence contact spin and charge densities at Fe sites in ferromagnetic Fe−Cr alloys are calculated using the discrete variational method. The hyperfine field at Fe nucleus is expressed as a linear sum of a core term, that is proportional to the local 3d moment, and a valence term, which is proportional to the valence spin density. The dependence of the hyperfine field, the contact charge density and the 4s magnetic moment on the number and orientation of chromium atoms in the first and second shells is studied. Comparison to experimental data is made.     

Mössbauer and magnetic investigation of Fe-Mn alloy

Mössbauer, X-ray, magnetization and susceptibility measurements were performed to study Fe_100–x Mn _x ,x=5, 15, 39, 50. The different phases of Fe-Mn were identified, and hyperfine interaction parameters and average magnetic moments of some samples were determined. The average hyperfine field and average magnetic moment decrease asx increases. The influence of the Mn neighbourhood on the derived parameters is discussed in the light of calculations using the first principle discrete variational method in the local density approximation.     

The hyperfine properties of a hydrogenated Fe/V superlattice

We study the effect of hydrogen on the electronic, magnetic and hyperfine structures of an iron-vanadium superlattice consisting of three Fe monolayers and nine V monolayers. The contact charge density (ρ), the contact hyperfine field (B_hf) and the electronic field gradient (EFG) at the Fe sites for different H locations and H fillings are calculated using the first principle full-potential linear-augmented-plane-wave (FP-LAPW) method. It is found that sizeable changes in the hyperfine properties are obtained only when H is in the interface region.