Nucleogenic iron studied by emission Mössbauer spectroscopy in Co-metal

Results obtained by means of the emission Mössbauer spectroscopy in metallic cobalt are reported. The Mössbauer line of the 14.4-keV energy connecting the first excited state of the stable ⁵⁷Fe nucleus with its ground state was used. Radioactive ⁵⁷Co was used as the precursor of the above nuclear state. It was dissolved in the natural metallic cobalt with the concentration of about 40 at. ppm including nucleogenic iron generated during decay of the cobalt precursor. Mössbauer spectra were collected in the temperature range between room temperature (RT) and 1075 K with the sample kept under vacuum. A transition from the low temperature hexagonal phase to the face centered cubic high temperature phase at about 690 K has no influence on the iron magnetic hyperfine field arising due to the ferromagnetic ordering of the host. On the other hand, the electron charge density on the iron nucleus has some relatively narrow maximum in the vicinity of the transition temperature. There is some discontinuity in the recoilless fraction as well indicating that the high temperature cubic phase provides somewhat stronger bonds for the isolated iron impurity. The anharmonic behavior of the lattice vibrations could be seen in the cubic phase well above the transition point. No measurable electric quadrupole interaction was found in the hexagonal phase. The evolution of the magnetic hyperfine field with the temperature is reasonably described by the spin wave formalism provided strong magnon-magnon scattering is allowed for. On the other hand, charge density on the iron nucleus follows thermal expansion except some singularity in the vicinity of the transition point.     

Magnetic ordering above room temperature in the sigma-phase of Fe66V34

Magnetic properties of four sigma-phase Fe_100−xV_x samples with 34.4?x?55.1 were investigated by Mössbauer spectroscopy and magnetic measurements in the temperature interval 4.2-300 K. Four magnetic quantities, viz. hyperfine field, Curie temperature, magnetic moment and susceptibility, were determined. The sample containing 34.4 at% V was revealed to exhibit the largest values found up to now for the sigma-phase for average hyperfine field, 〈B〉=12.1 T, average magnetic moment per Fe atom, 〈μ〉=0.89 μ_B, and Curie temperature, T_C=315.3 K. The quantities were shown to be strongly correlated with each other. In particular, T_C is linearly correlated with 〈μ〉 with a slope of 406.5 K/μ_B, as well as 〈B〉 is so correlated with 〈μ〉, yielding 14.3 T/μ_B for the hyperfine coupling constant.     

Mössbauer study of Fe0.92−xCoxP0.08 nanowire arrays

Arrays of Fe_0.92−xCo_xP_0.08 (0.22≤x≤0.78) ternary alloy nanowires were fabricated in anodic aluminium oxide templates by electrochemical deposition. The broadened peaks in transmission Mössbauer spectra and the halo in selected area electron diffraction patterns indicate that the structure of Fe_0.92−xCo_xP_0.08 nanowires is amorphous. However, the short-range order of Fe_0.92−xCo_xP_0.08 nanowires has a bcc structure with a [110]-preferred orientation that is parallel to the nanowires. The magnetic texture results in the magnetic moment direction of the Fe atoms being along the nanowires. The short-range order around the Fe atoms reaches a minimum at x=0.45. With increasing Co content, the average hyperfine field decreases, while the isomer shift and quadrupole splitting remain almost constant, which result from the variation of 3d and 4s electron volume density at the Fe sites.     

A Mössbauer study of the chemical stability of iron oxide nanoparticles in PMMA and PVB beads

We have prepared magnetic beads consisting of iron oxide nanoparticles in a polymethyl methacrylate (PMMA) and a polyvinyl butyral (PVB) matrix. High-field Mössbauer studies show that the particles have an almost perfect collinear spin structure and magnetization measurements show that they are superparamagnetic at room temperature at a time scale of seconds. We have followed the oxidation of the particles, which initially have a stoichiometry close to magnetite. The oxidation is fast during the first 2–3 weeks and then continues slowly such that even after 30 weeks the particles have not completely transformed to maghemite. The PVB beads are hydrophilic and biocompatible and are therefore well suited for applications in medicine and biology.     

Size dependence of the Mössbauer effect in one-dimension

Employing a model of coupled harmonic oscillators we analyze the nature of recoilless emission in the Mössbauer effect for a finite sized 1D lattice. We demonstrate explicitly that under certain assumptions, recoilless probability first attains a maximum for a certain lattice size and then decreases with increasing lattice size. Further, we derive a scaling relation for this variation. Our treatment may have relevance to the recoilless probability in finite clusters such as nanocrystals and nanowires.     

Eu and Fe Mössbauer study of mechanically alloyed EuFeO3

EuFeO₃ was prepared by mechanical alloying starting from europium and iron oxides. After 20 h of milling the resulting compound is pure EuFeO₃. Samples were studied as a function of milling period using XRD, Mössbauer, SEM, and magnetic measurements. Mössbauer spectroscopy was used to probe both the transition metal and the rare-earth sites. Results are compared with previous works on EuFeO₃ prepared by different methods.     

Mössbauer characterization of tin dopant ions in the antiferromagnetic ilmenite MnTiO3

Mössbauer parameters of ¹¹⁹Sn diamagnetic dopant cations in an antiferromagnetic compound having the ilmenite structure are for the first time reported. The spectra reveal a well resolved hyperfine splitting pattern of combined magnetic and quadrupole interactions (at 5 K, δ=0.19 mm/s, H₁=52.5 kOe, eV_ZZQ_3/2=−0.80 mm/s, θ≈0°). This spectral component whose contribution (A₁=82%) represents more than four fifths of the total amount of the dopant (Sn/(Mn+Ti)=1/200) is assigned to Sn(IV) ions located in the bulk of MnTiO₃, on the Mn(II) site, and with a Mn(II) vacancy in their nearest surrounding. Two spectral components with minor contributions are also observed: one of them (H₂≈25 kOe, A₂=8%) can be assigned to Sn(IV) ions, in the MnTiO₃ lattice as well, on a site where they exhibit a weaker spin polarization (this site could be the Ti(IV) one) and the other (H₃=0 kOe, A₃=10%) to SnO₂ or/and Ti_1−xSn_xO₂ clusters. The Néel temperature of MnTiO₃ probed by the ¹¹⁹Sn dopant (T_N=69±2 K) agrees well with the values previously provided by ESR and antiferromagnetic resonance measurements. Variation of H₁ with temperature follows close the Brillouin function for S=5/2. No perturbation appears in the Mössbauer spectra around T=90 K where a broad peak, characteristic of 2D magnetic interactions, is observed on the static magnetic susceptibility curve.     

Zero-field and in-field Mössbauer spectroscopy as a tool for structural and magnetic characterization of maghemite (γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) nanoparticles

Nowadays, nanoparticles of maghemite (γ-Fe₂O₃) represent one of the most useful materials in modern advanced nanotechnological applications due to their superior magnetic properties. For their characterization,⁵⁷Fe zero-field and in-field Mössbauer spectroscopy have proved themselves to be very powerful and effective tools which are crucial for an investigation of the local surrounding of iron atoms and observation of dynamic effects. The structural and magnetic characteristics of maghemite and its nanoparticles are thus discussed with regard to their zero-field and in-field Mössbauer spectra recorded at various temperatures and applied external magnetic fields. In addition, a special attention is also devoted to remarkable physical phenomena (superparamagnetism, spin canting) occurring largely in maghemite nanosized particles.     

EPR study of the low temperature ferroelectric phase transition in Cu doped Rb2ZnCl4 single crystals

Temperature dependent EPR measurements on copper doped Rb₂ZnCl₄ single crystals allowed us to evidence and study the P2₁cn↔C1c1 structural phase transition that takes place in this compound at 74.6 K. From the two types of Cu²⁺ centers localized at different anionic sites, called Cu²⁺(I) and Cu²⁺(II), which are formed in this compound, only the Cu²⁺(II) centers exhibit observable changes in their EPR spectra, attributable to the symmetry lowering. The observed changes have been related to the soft-mode responsible for the structural phase transition.     

57Fe Mössbauer study of YBa4Cu2.95Fe0.05O8.5+y

⁵⁷Fe Mössbauer measurements were performed on the Fe-doped YBa₄Cu₃O_8.5+y compound as a function of annealing temperature in vacuum. Mössbauer spectra were analyzed using three different quadrupole split doublets. The resistance measurements showed that the compound is not superconducting. The possible identification of the Cu sites with their nearest neighbor oxygen sites in this compound is suggested. Comparison of the results with data of the presence of the superconductor YBa₂Cu₃O₇ allows us to suppose that the presence of the Cu-chain sites alone does not result in superconductivity.     

Tin(IV) derivatives of 2,6-pyridinedicarboxylate: A Sn Mössbauer spectroscopic investigation

A series of organotin(IV) derivatives of 2,6-pyridinedicarboxylate has been investigated by Mössbauer spectroscopy in order to elucidate aspects concerning bonding and structural features in the solid state. A geometrical pattern of five-fold coordination at the metal centre has been revealed for SnCl₃Bu and SnClBu₃ derivatives. Trans stereochemistry for the butyl and vinyl groups of SnCl₂Bu₂ and SnCl₂(Vin)₂ derivatives has also been identified by this method. The isomer shift for the divinyl derivative is concurrent to a 7-coordinate metal centre contrasting to that for the dibutyl one. Although there is a discrepancy in isomer shift between these compounds, both have seven-fold coordination at the Sn(IV) nucleus. The resulting data has given evidence that 2,6-pyridinedicarboxylate is acting as a tridentate ligand through pyridil and carbolxylate moiety to all derivatives except for SnClBu₃. For the latter, the coordination mode occurs via carboxylate groups. The overall data support distorted geometrical pattern to all complexes in solid state.     

Investigation of the seeding-layer effect for a ferroelectric thin film with the transverse Ising model

The transition feature of a ferroelectric thin film with a seeding layer is studied based on the transverse Ising model. The influence of the seeding layer on the transition behavior of a ferroelectric thin film is investigated systemically, and the effect of the interaction parameters for the seeding layer on the phase diagram is also obtained. Meanwhile, the polarization and Curie temperature of the ferroelectric thin film are calculated for different seeding-layer structures. The results show that the polarization and Curie temperature of the film will be obviously modified on adding a seeding layer.     

Study of domain structure of magnetic powder particles by Mössbauer spectroscopy

The determination technique of monodomain state of the magnetic powder particles using the Mössbauer spectroscopy is described. The method was verified on the particles of gadolinium iron garnet near the compensation temperature. It has also shown that using the Mössbauer spectroscopy we can evaluate the domain wall energy in ferrites possessing the compensation point.     

Study of the magnetic properties of the permanent magnets by Mössbauer spectroscopy

This paper presents methods that can be used in order to determine the relative remanent magnetization and uniaxial magnetic anisotropy constant of particles in powder-based permanent magnets using Mössbauer spectroscopy. The methods were verified on the permanent magnet barium ferrite.     

Dielectric properties and phase transitions of (Pb0.87La0.02Ba0.1)(Zr0.6Sn0.4−xTix)O3 ceramics with compositions near AFE/RFE phase boundary

The electrical properties and phase transition behavior of (Pb_0.87La_0.02Ba_0.1)(Zr_0.6Sn_0.4−xTi_x)O₃ solid solutions (PLBZST, 0.04≤x0.2) were investigated by the X-ray diffraction, permittivity, pyroelectric current, and P-E electric hysterisis loops. As the composition x increased from 0.04 to 0.2, the antiferroelectric ceramics (x≤0.07, AFE) with tetragonal phase changed to the ferroelectric relaxors (RFE, 0.09≤x). AFE ceramics showed a peculiar diffuse phase transition and dielectric relaxation at the low temperature (down to −100 °C) due to a frustration between AFE and FE state. With an increase in composition x, electrically field-induced AFE-FE switching field (E_AFE-FE) and AFE-paraelectric (PE) phase transition temperature (T_c) are depressed in the temperature (T)-Ti composition (x) phase diagram, a FE-AFE-PE triple phase point (T_tr) with the lowest transition temperature occurred at x=0.09. The pyroelectric currents under an application of various external electric field (E) were measured to identify a T-E phase diagram of the PLBZST compound.     

Mössbauer studies on the superparamagnetic behavior of CoFe2O4 with a few nanometers

CoFe₂O₄ nanoparticles with a cubic spinel structure are prepared by a high-temperature thermal decomposition method. The average particle sizes are 4.6  and 5.7 nm for CoFe₂O₄ made with two kinds of solvents by TEM. Mössbauer spectra of 4.6 nm particles displayed a superparamagnetic behavior as demonstrated by a single line with zero hyperfine fields, but that of 5.7 nm particles did not at room temperature. It is considered that anisotropy energy was still more superior to thermal energy because of particle size of 5.7 nm CoFe₂O₄. Furthermore, Mössbauer spectra exhibited the typical spectrum shapes of the CoFe₂O₄ at 4.2 K. The spectrum at 4.2 K was fitted using two magnetic components of hyperfine fields _Hhf=540.4,512.6$H_{\mathrm{hf}}=540.4,512.6$ kOe and isomer shifts δ=0.40,0.30$\delta =0.40,0.30$ mm/s for 4.6 nm and _Hhf=542.7,512.8$H_{\mathrm{hf}}=542.7,512.8$ kOe and δ=0.41,0.29$\delta =0.41,0.29$ mm/s for 5.7 nm corresponding to Fe³⁺ ions at site A and site B, respectively.     

Mössbauer spectroscopy as a probe of magnetic states in La0.5Ca0.5FeO3−δ perovskite

Charge disproportionation in La_0.5Ca_0.5FeO_3−δ perovskite has been detected by zero-field Mössbauer spectra from 20 K to room temperature. On the basis of the parameters of center shifts and hyperfine fields, Mössbauer spectra identified that the iron ionic states are Fe³⁺ and Fe⁵⁺ below 150 K, Fe³⁺, Fe⁴⁺ and Fe⁵⁺ in the intermediate temperature region, as well as Fe³⁺ and Fe⁴⁺ above 220 K. At low temperatures, the system exhibits a cluster-glass-like state resulting from competition between antiferromagnetic interaction of Fe³⁺–Fe³⁺ and ferromagnetic interaction of Fe³⁺–Fe⁵⁺.     

Mössbauer study of the pulsed laser deposition of polycrystalline magnetic films

Polycrystalline magnetite films were grown by pulsed laser deposition from an α-Fe₂O₃ target at 450 °C. X-ray diffraction analysis showed the presence of a single-phase spinel film with preferred orientation when the deposition was performed at low oxygen pressure. Mössbauer spectroscopy at both room temperature and 120 K was used to identify the hyperfine parameters of the magnetite film deposited on glass at 450 °C and at an oxygen partial pressure of 10⁻⁴ Torr.     

X-ray diffraction analysis of the modulated structure of Bi2Sr2CaFe2O y

The modulated structure of the Bi₂Sr₂CaFe₂O _y compound isomorphous with the Bi₂Sr₂CaCu₂O _y phase was refined by the method of the full profile analysis on the basis of the powder X-ray diffraction data. The analysis was carried out in the superspace group ofN:Abmm: 1 – 11 using the parameters of the unit cell of the basic structurea = 5.466(3),b = 5.446(5) andc = 31.25(9) Å and the modulation vectorq = 0.220(5)b* +c*. The model of excess oxygen interstitials into the BiO plane was used by applying a saw-tooth-type function of the form:U = 2U ₀ [(X ₄ -X ₄ ⁰ /)] [1]. The results point to a strong displacement of the atoms from their positions in the basic structure. An essential improvement of theR factors was obtained by taking into account the modulation waves of the higher harmonics.     

Fe-contacts on InAs(100) and InP(100) characterised by conversion electron Mössbauer spectroscopy

We have grown 4 nm thin films of ⁵⁷Fe on InAs(100) and InP(100) surfaces by use of MBE and studied the samples by ⁵⁷Fe conversion electron Mössbauer spectroscopy. In the case of InAs, the Mössbauer spectrum showed a sextet due to α-Fe and a further magnetically split component with slightly smaller hyperfine field, which is attributed to interface components. This result indicates that there is a relatively sharp interface between Fe and InAs. On the contrary, the spectrum of the InP sample showed a sextet with very broad lines and a smaller average hyperfine field. This suggests a strong chemical reaction between iron and the substrate, which results in the formation of a poorly crystalline phase.