Evaluation of the Debye temperature for iron cores in human liver ferritin and its pharmaceutical analogue, Ferrum Lek, using Mössbauer spectroscopy.

An iron-polymaltose complex, Ferrum Lek, used as antianemic drug and considered as a ferritin analogue and human liver ferritin were investigated in the temperature range of 295-90K using (57)Fe Mössbauer spectroscopy with a high velocity resolution (in 4096 channels). This study aimed to make a comparison of the Fe atom dynamics in the Ferrum Lek and ferritin iron cores by means of evaluation of the Debye temperature using the temperature dependence of the spectral center shift obtained with two different fitting procedures and the second order Doppler shift approach. The Debye temperature, evaluated as ΘD=502±24K for Ferrum Lek and ΘD=461±16K for human liver ferritin, demonstrated a very small difference in the Fe atom vibrations, reflecting a slightly smaller rigidity in the iron cores in human liver ferritin.

Comparative study of the iron cores in human liver ferritin, its pharmaceutical models and ferritin in chicken liver and spleen tissues using Mössbauer spectroscopy with a high velocity resolution.

Application of Mössbauer spectroscopy with a high velocity resolution (4096 channels) for comparative analysis of iron cores in a human liver ferritin and its pharmaceutically important models Imferon, Maltofer(®) and Ferrum Lek as well as in iron storage proteins in chicken liver and spleen tissues allowed to reveal small variations in the (57)Fe hyperfine parameters related to differences in the iron core structure. Moreover, it was shown that the best fit of Mössbauer spectra of these samples required different number of components. The latter may indicate that the real iron core structure is more complex than that following from a simple core-shell model. The effect of different living conditions and age on the iron core in chicken liver was also considered.

Extended scaling in the magnetic critical phenomenology of the σ-phase Fe0.53-Cr0.47 and Fe0.52-V0.48 alloys.

The magnetization of the sigma-phase Fe(0.53)Cr(0.47) and Fe(0.52)V(0.48) alloys was studied as a function of temperature and field. The experiments show that both materials behave magnetically as re-entrant spin glass systems. Field versus temperature diagrams were obtained where the locations of the paramagnetic phase, the intermediate ferromagnetic-like phase and the spin glass fundamental state were displayed. These diagrams are in qualitative agreement with the predictions of the mean field theory for the interplay between the ferromagnetic and spin glass orderings. The critical phenomenology near the para-ferromagnetic transition could be investigated. It was found that the paramagnetic susceptibility is quite well described by the extended scaling scheme, where the reduced temperature is written as τ = (T - T(c))/T. The value obtained for the susceptibility critical exponent γ is intermediate between the prediction of the 3D Heisenberg universality class and the large values observed in spin glasses, as previously found in other re-entrant systems. The data do not confirm the validity of the extended scaling in the ferromagnetic-like phase. Using either the conventional or extended scaling protocols, the exponents ß and δ were found to have values close to those reported for spin glass transitions. Despite the relevance of disorder and the anomalous values determined for ß, γ and δ, the Widom scaling relation holds as an equality.

Vibrational properties of alpha- and sigma-phase Fe-Cr alloy.

Experimental and theoretical studies, of the Fe-partial phonon density of states (PDOS) for Fe52.5Cr47.5 alloy having alpha and sigma phases were carried out. The former using the nuclear resonant inelastic x-ray scattering method, and the latter with the direct one. Characteristic features of PDOS, which distinguish one phase from the other, were revealed and successfully reproduced by the theory. Data pertinent to the dynamics such as the Lamb-Mössbauer factor, f, the kinetic energy per atom, E(k), and the mean force constant, D, were directly derived, while vibrational specific heat at constant volume, C(V), and vibrational entropy, S were calculated using the Fe partial PDOS. Based on the values of f and C(V), we determined Debye temperatures, Theta(D). An excellent agreement for some quantities derived from experiment and first-principles theory, like C(V) and quite good ones for others like D and S were obtained.

Debye temperature of disordered bcc-Fe-Cr alloys.

The Debye temperature, Θ(D), of Fe(100-x)Cr(x) disordered alloys with 0 ≤ x ≤ 99.9 was determined from the temperature dependence of the centre shift of (57)Fe Mössbauer spectra recorded in the temperature range of 60-300 K. Its compositional dependence shows an interesting non-monotonous behaviour. For 0

Unusual dynamics of Fe atoms in a chromium matrix.

(57)Fe site Mössbauer spectroscopy (MS) was used to investigate the dynamics of (57)Fe atoms embedded in a chromium lattice as impurities. From the Mössbauer spectra recorded in the temperature range of 80-350 K, a temperature dependence of the Lamb-Mössbauer factor, f, was determined. The latter revealed an unusual dynamics of (57)Fe atoms, namely a harmonic mode below T≈145 K with a characteristic effective Debye temperature Θ(eff) = 190.2 K and a strongly anharmonic one above T≈145 K. The latter mode exists in two clearly defined temperature intervals with significantly different Θ(eff) values, namely (i) ∼155 K for ∼145 K ≤ T ≤ ∼240 K and the record-high anharmonic coefficient ε = -25.8 × 10(-4) K(-1), and (ii) ∼151 K for T ≥ ∼240 K with ε = -14 × 10(-4) K(-1). Based on Visscher's theory, the record-low value of the relative binding force constant for Fe atoms was determined as 0.0997 for the harmonic regime. It is suggested that the unusual dynamics observed in this study might be related to the underlying spin-, charge- and strain-density waves of chromium.

Electronic structure of a σ-FeCr compound.

The electronic structure of a σ-FeCr compound in a paramagnetic state was calculated for the first time in terms of isomer shifts and quadrupole splittings. The former were calculated using the charge self-consistent Korringa-Kohn-Rostoker (KKR) Green's function technique, while the latter were estimated from an extended point charge model. The calculated quantities combined with recently measured site occupancies were successfully used to analyze a Mössbauer spectrum recorded at room temperature using only five fitting parameters namely background, total intensity, linewidth, IS0 (necessary to adjust the refined spectrum to the used Mössbauer source) and the QS proportionality factor. Theoretically determined changes of the isomer shift for the σ-FeCr sample were found to be in line with the corresponding ones measured on a α-FeCr sample.

Magnetic properties of human liver and brain ferritin.

Human brain (globus pallidus) and liver tissues were investigated by means of electron microscopy (EM), Mössbauer spectroscopy (MS) and SQUID magnetometry techniques. Based on MS measurements, the iron present was identified to be in the ferritin-like form (61-88%) and in the form of a low-spin iron species (the balance). Its overall concentration was estimated as 1.5(3) mg in the brain and 2.4(5) mg in the liver, per gram of lyophilized tissue. The average core diameter was determined by EM measurements to be equal to 7.5(1.3) nm for the liver and 3.3(5) nm for the brain. Magnetization measurements carried out between 5 and 300 K yielded an estimation of an average blocking temperature, (TB), as equal to 6.7 K and 8.5 K for the liver and the brain, respectively. From the dependence of (TB) on the external magnetic field it was concluded that the ferritin-like cores in the studied samples can be regarded as non-interacting particles. Finally, the uniaxial magnetic anisotropy constant was determined to be 6 x 10(3) J/m3 for the liver and 4 x 10(4) J/m3 for the brain.