Fe-Fe Interactions Research Articles

A comparison of an undecairon(III) complex with the ferritin iron core

The iron core of ferritin is comprised of up to 4,500 Fe(III) atoms as Fe 2O 3·nH 2O, which is maintained in solution by a surrounding, spherical coat of protein. Organisms as diverse as bacteria and man use the ferritin iron-protein complex as a reservoir of stored iron for other essential proteins. To extend studies of the steps in polynuclear iron core formation, a recently characterized undecairon(III) oxo-hydroxo aggregate [Fe 11 complex] (Gonin et al., J. Am. Chem. Soc. 109, 3337 [1987]) was examined by x-ray absorption spectroscopy as a model for an intermediate. The results, which are comparable to the previous x-ray diffraction studies, show near neighbors (Fe-O) at 1.90 Å that are distinct from those in ferritin and a longer distance of 2.02 Å. However, contributions from neighbors (Fe-C) known to exist at ca. 2.7 Å were obscured by a highly ordered Fe-Fe interaction and were not detectable in the Fe 11 complex in contrast to a previously characterized Fe(III) cluster bound to the protein coat. Of the two Fe-Fe interactions detectable in the Fe 11 complex, the shortest, at 3.0 Å is particularly interesting, occurring at the same distance as a full shell (CN = 6) in ferritin, but having fewer Fe neighbors (CN = 2–3) characteristic of an intermediate in core formation. The incomplete Fe-Fe shell is much more ordered than in ferritin, suggesting that the disorder in ferritin cores may be associated with the later steps of the core growth. Differences between the Fe 11 complex and the full core of ferritin indicate the possibility of intermediates in ferritin iron formation that might be like Fe 11.

The antiferromagnetism in YBa 2Cu 3O 6+δ studied by Mössbauer spectroscopy

A small amount of 57Fe (about 0.3%) was used to substitute for Cu in the Y-Ba-Cu-O 1-2-3 compounds. With this small amount of Fe, the possibility of Fe-Fe interactions can be ignored and the 57Fe ions serve only as a probe to study the magnetic structure of the high T c superconductor compounds. As a result of annealing samples in flowing Ar gas at 750°C for 10 h, about 30% of the iron ions migrate from Cu(1) sites to Cu(2) sites. The Mössbauer spectrum of the Fe at the Cu(2) site shows that the Cu(2)-O 2 is antiferromagnetically ordered which agrees with the neutron diffraction result. The temperature dependence of the hyperfine field of the magnetic component follows a T 3/2 law, indicating a 3 dimensional spin wave excitation. This is consistent with the magnetic ordering of the Fe probe at the Cu(1) site which we observe at 4.2 K. The analysis of the Mössbauer spectra at different temperatures and with different oxygen deficiencies are also discussed.

Magnetism of iron-sulfur tetrahedral frameworks in compounds with thallium I. Chain structures

The ternary iron sulfides, monoclinic TlFeS 2 (linear tetrahedral chains) and orthorhombic Tl 3Fe 2S 4 (folded tetrahedral chains), have been investigated by means of magnetic susceptibility measurements, powder neutron diffraction, and Mössbauer spectroscopy. Both compounds exhibit three-dimensional antiferromagnetic order with Néel temperatures of 190(10) and 90(5) K, respectively. The low-temperature magnetic structures have been obtained and the moment values are 1.85(6) μ B for TlFeS 2 and 1.5(2) μ B for Tl 3Fe 2S 4. The magnitude and the coupling of moments in the Fe-S tetrahedral frameworks are seen to be strongly influenced by direct Fe-Fe interactions for edge-sharing tetrahedra, while the Fe-S bond may be described as ionic. The Fe-Fe interaction apparently goes along with a metallic state, permitting an intermediate valence (Fe 2.5+) in the folded chain compound.

Electronic band structure of tetrahedral iron sulphides

The electronic band structures of cubic and tetragonal iron monosulphide have been obtained for self-consistent linear muffin-tin orbital calculations within the atomic sphere and local density approximations. The Fe-S bond is seen to be mainly ionic with little covalent mixing. In calculations excluding spin polarisation, both sulphides are found to be metallic with conduction bands of mainly d character, but the densities of states at the Fermi level differ significantly. The low value of the tetragonal sulphide, which is due to a rearrangement of the d bands by direct Fe-Fe interactions for edge-sharing FeS4 tetrahedra, renders this phase nonmagnetic. With ferromagnetic spin polarisation, for the cubic sulphide the authors obtain a moment of 3.34 mu B while the phase remains metallic.

Magnetic Properties of YFe, (Gd, Tb)¿YFe Sputtered Films

YFe sputtered films were studied to clarify the behavior of Fe-Fe interactions in an amorphous RE-Fe matrix. The effect of the RE magnetism on the magnetic properties of RE-Fe films was also investigated using (Gd, Tb)-YFe sputtered films. Amorphous YFe films exhibit spin-glass like characteristics, that is, the magnetization does not saturate easily even at low temperatures because of the noncollinear alignment of the Fe moments. The addition of an RE element (Gd, Tb) to YFe film serves to eliminate the spin-glass like nature, and a magnetically ordered state can be observed. The exchange interaction between the RE element and Fe may play an important role in RE-YFe film.

Magnetic properties of Y-Fe films sputtered with substrate bias

YFe sputtered films were investigated to clarify the behavior of Fe-Fe interaction. The efect of compositional inhomogeneity on Fe magnetism was also investigated using bias-sputtered YFe films. Amorphous YFe films indicate the spin-glass like characteristics, that is, their magnetization is hard to saturate for applied magnetic field even at low temperature because of the non-collinear alignment of the Fe moment. The application of the substrate bias voltage causes the preferential resputtering of Y and Fe-rich phase. Fe-rich phase eliminates the spin-glass like nature and the magnetically ordered state can be observed.

ＹＦｅ，（Ｇｄ，Ｔｂ）‐ＹＦｅスパッタ膜の磁気的性質

YFe sputtered films were investigated to clarify the behavior of Fe-Fe interaction in amorphous RE-Fe matrix. The effect of RE magnetism on magnetic properties of RE-Fe films was also investigated using (Gd, Tb)-YFe sputtered films. Amorphous YFe films indicate the spin-glass like characteristics, that is, their magnetization is hard to saturate even at low temperature because of the non-collinear alignment of the Fe moment. The addition of RE element (=Gd, Tb) to YFe film eliminates the spin-glass like nature and the magnetically ordered state can be observed. The exchange interaction between RE and Fe may play an important role in RE-YFe film.

Magnetic properties of natural and synthetic wolframites Fe x Mn1?x WO4

We report in the present paper the main results concerning the evolution of the structural, magnetic and hyperfine properties of natural and synthetic wolframites Fe x Mn1−x WO4 in the composition range 0.16 0.3 ( $$\bar \eta$$ ≃0.7). In addition we discuss the variation of the magnitude of H hf and of the angle ϑ between the H hf direction and the principal axis of the electric field gradient (EFG) V zz with the iron content. A single crystal Mossbauer study has also been performed to determine the orientation of the principal axis of the EFG and of the H hf direction relative to the crystallographic axes. Mossbauer spectroscopy and magnetic susceptibility techniques have been used to obtain the magnetic ordering temperature T N. One finds a linear variation of T N with x for 0.4<x<1 and a deviation from the linear behavior for 0.16<x<0.3. These results are discussed in terms of the contributions of the different Fe-Fe, Fe-Mn and Mn-Mn exchange interactions.

Inelastic neutron scattering in amorphousFe0.78P0.22and crystallineFe3P systems

Pulsed inelastic neutron scattering measurements have been performed on amorphous a-${\mathrm{Fe}}_{0.78}$${\mathrm{P}}_{0.22}$ and its crystalline counterpart, c-${\mathrm{Fe}}_{3}$P. Measurements of the generalized distribution function G(Q,E) for Q=5--9 A${\r{}}^{\mathrm{\ensuremath{-}}1}$ were employed to determine G(E), the neutron-weighted density of states. The a-${\mathrm{Fe}}_{0.78}$${\mathrm{P}}_{0.22}$ results indicate a low-energy Fe-Fe derived band and a distinct high-energy Fe-P, opticlike band. This contrasts with amorphous metal-metal alloys which exhibit a single low-frequency peak in the phonon spectrum. A comparison with theoretical calculations of the neutron-weighted partial densities of states indicates very good qualitative agreement in band shape and relative intensities. Differences in the peak positions are attributed to weaker Fe-Fe and Fe-P interactions. The results are consistent with similar short-range order in a-${\mathrm{Fe}}_{0.78}$${\mathrm{P}}_{0.22}$ and c-${\mathrm{Fe}}_{3}$P. Similarities between the low-energy experimental a-${\mathrm{Fe}}_{0.78}$${\mathrm{P}}_{0.22}$ and theoretical a-Fe spectra are also noted.

Magnetic properties of Fe-Ni invar alloy films

A detailed experimental study of the Invar alloy films show that the behaviour of γ-phase Fe-Ni films resembles that of Y-Fe-Ni amorphous film, that is, ∂ M s/∂ T is constant. This phenomenon is discussed by the environmental effect of Fe-Fe pair interaction in the inhomogeneous state.

Heat capacity and solid solubility of iron in scandium

The maximum solid solubility of iron in scandium was determined to be between 50 and 85 at.ppm in the as-cast condition. As the concentration of iron increases, it segregates along the grain boundary, as is evident from optical metallography and electron microprobe examinations. Annealing also causes the iron dissolved in scandium to separate out and cluster along the grain boundary. Heat capacity measurements show an anomaly in the C T versus T 2 plots for iron concentrations of 19 at.ppm or greater. For iron dissolved in solid scandium the excess entropy due to the iron impurity is in agreement with the theoretical prediction of ck ln(2 S + 1) for an impurity-conduction electron (Kondo) interaction, but is 4–8 times larger than the theoretical prediction when iron segregates along the grain boundary. Furthermore, our results suggest that most of the previously reported low temperature physical properties of scandium are probably in error because of either iron impurity-conduction electron interactions or Fe-Fe interactions in the precipitated second-phase Sc-Fe compound.

Vibrational spectrum of amorphous metallic alloy Fe100-xPx

The vibrational spectrum is investigated for the realistic models of amorphous metallic alloy Fe100-xPx. It is shown that the vibrational spectrum has two peaks. The high-frequency and low-frequency peaks are caused by the Fe-P and the Fe-Fe interaction, respectively; the former is interpreted as being due to the localised optical vibrational mode and the latter to the acoustic one. The first moment and the sound velocity in amorphous systems are reduced by about 10% in comparison with those in crystal. This is understood in terms of larger atomic volume in amorphous systems.

Low lying excitations of Fe2+ions in the mixed antiferromagnet Fe1-xMnxCl2(Raman scattering study)

Electronic excitations within the 5T2g manifold of Fe2+ ions in the mixed crystals Fe1-xMnxCl2 have been measured by Raman scattering for temperatures T>or<TN. In the paramagnetic phase, the electronic transition energies decrease linearly in x for 0<x<or approximately=0.75 but level off and increase slightly in the dilute limit. For 0<x<or approximately=0.75 the position and concentration dependence of observed transitions are successfully predicted using a single-ion effective Hamiltonian model which assumes that the Fe2+ ion environment in the disordered crystal can be represented by an average crystalline potential. The dominance of Fe-Fe interactions is illustrated by the change in behaviour at x approximately=0.75 which is close to the percolation limit for this crystal structure. For T<TN the single-ion model is extended within a molecular field approximation to describe the linear concentration dependence of the exciton frequencies. The magnon frequency also has a linear, though different, dependence on x. The electron-phonon coupling observed in FeCl2 (Johnstone et al., 1978) is now found to be more complicated than previously thought, comprising a three-level interaction of two electronic bands with the Eg phonon.

Theory of volume anomalies in magnetic transition metal alloys

The electronic contribution to the pressures which determines the equilibrium volume of transition metals is parametrized by use of the interacting Anderson model. It is discussed that there are two mechanisms which can explain the volume anomalies in the Invar alloys. The Fe-Fe atomic interaction which seems to be important in the Invar effect is also discussed.

Magnetic properties of RE(FexRh1-x)2, RE = Y, Gd, Dy, Ho

YRh2 can be characterized as a Pauli-paramagnet. At 4 K no ordering temperatures could be detected for Y(Fe, Rh)2 from bulk magnetic measurements, whereas at 5 K the 57Fe Mossbauer investigations reveal magnetic hyperfine interactions. For RE = Gd, Dy, Ho a ferrimagnetic coupling is observed in the Fe substituted compounds. The Curie temperatures can be analyzed for constant x using a de Gennes function. The concentration dependence of Tc might be explained by a distance dependent Fe-Fe interaction.

Spin-Orientation Diagrams and Magnetic Anisotropy of Rare-Earth-Iron Ternary Cubic Laves Compounds

The directions of the easy magnetization in the ${\mathrm{Ho}}_{x}{\mathrm{Tb}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{2}$, ${\mathrm{Ho}}_{x}{\mathrm{Er}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{2}$, ${\mathrm{Dy}}_{x}{\mathrm{Tb}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{2}$, ${\mathrm{Dy}}_{x}{\mathrm{Er}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{2}$, and ${\mathrm{Ho}}_{x}{\mathrm{Tm}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{2}$ systems have been determined, as a function of $x$ and temperature by means of the M\"ossbauer effect in $^{57}\mathrm{Fe}$. If the direction of magnetization of each system is described by a ($x,T$) spin-orientation diagram, it is found that the ($x,T$) plane is divided into two or three regions, in each of which the direction of magnetization is along a different major crystal axis. Theoretical calculations based on the assumption that the magnetic crystalline anisotropy is due to the anisotropy of the interaction between the $4f$ electrons of the rare-earth ions with the crystal fields reproduced the general features of the experimental results though small discrepancies remained. Taking into account an additional contribution to the anisotropy attributed to the Fe-Fe interaction improved the agreement between the theoretical and experimental spin-orientation diagrams. From the theoretical fits to the experimental results a value of $(\ensuremath{-}0.038\ifmmode\pm\else\textpm\fi{}0.003){a}_{0}^{\ensuremath{-}2}$ is derived for the ratio of the crystal field parameters $\frac{{A}_{6}}{{A}_{4}}$. The transitions between the regions of the spin-orientation diagrams are not sharp. Possible reasons for the existence of the transition regions are discussed.

Effects of Atomic Ordering on the Curie Temperature of Fe3Pt

The ferrromagnetic Curie temperatures were measured for ordered and disordered phases of Fe 1- x Pt x (0.25≤ x ≤0.30). The effect of atomic ordering on the Curie temperature was discussed by a pair-interaction model. It was concluded that Fe-Fe pair interaction is negative when only the nearest neighbor pair interactions were taken into account.

The thermoelectric power of dilute gold-iron alloys

We have measured the thermoelectric power of a number of Au-Fe alloys, with Fe concentrations between similar 10 and 1900 ppm. Measurements were made between 0.4 and 30 K in fields up to 70 kOe. The alloys exhibited the familar `giant' thermopower in zero field, the peak value observed being - 15 μ V K-1 at about 10 K. Both the order of magnitude and the temperature dependence of the zero-field thermopower agree fairly well with Kondo's theory of spin-flip scattering. The thermopower of all but the most dilute alloys shows an initial increase in a magnetic field, which we believe is caused by Fe-Fe interactions. The thermopower then decreases due to `freezing-out' of spin-flip scattering and a simple pair-interaction model accounts for most of this observed behaviour. For the most concentrated alloy the decrease is not observed, even for the maximum field applied. For still higher fields (and lower concentrations) the thermopower decreases approximately as 1/H, as is suggested by a recent perturbation calculation.

Single-Impurity and Interaction Effect on the Host NMR Linewidth ofCuFein the Kondo State

The effects of single Fe impurities on the Cu-host NMR in $\mathrm{Cu}\mathrm{Fe}$ have been measured over a wide range of Fe concentrations up to 45 kOe at 1.65\ifmmode^\circ\else\textdegree\fi{}K. The additional impurity $d$-spin conduction-electron spin-correlation effects on the host NMR linewidth originally noted by Golibersuch and Heeger have been shown to be the result of single Fe impurities in the Kondo state; these effects are destroyed at lower applied fields with increasing Fe concentration as a result of Fe-Fe interactions.

NEUTRON DIFFRACTION STUDY OF ErFe2

Cubic Laves phase compounds (MgCu2-structure) involving rare earths have received considerable attention recently. We have undertaken neutron diffraction measurements on powder ErFe2 between 4.2 and 680oK. The temperature dependence of the sublattice magnetization has been determined from the temperature dependence of the individual magnetic reflections, which are sensitive to either Er, Fe, or (Er+Fe) and (Er−Fe). The magnetic properties of ErFe2 will be discussed in terms of three molecular field parameters. It is concluded that the Er-Er interaction decreases rapidly with increasing temperature and that the Er-Fe interaction strongly affects the values of the erbium sublattice moment between 350 and 600oK. The Fe-Fe interaction seems to dominate and tends to mask the Er-Fe and the Er-Er effects.