Crystal structure and Mössbauer spectroscopic study of FeSnF6·6H2O

Large single crystals of FeSnF₆·6H₂O were grown when aqueous hydrofluoric solutions of SnF₂ and FeF₂ were allowed to evaporate in air. Tin-119 Mössbauer spectroscopy at ambient temperature shows a single line at slightly negative isomer shift relative to CaSnO₃ at room temperature (=–0.380(6) mm/s, =0). This is characteristic of tetravalent tin octahedrally coordinated by fluorine. The X-ray crystal structure shows that tin(IV) is coordinated by 6 fluorine atoms, and Fe(II) by 6 water molecules. Both sites show a slight distortion from octahedral symmetry: the six distances are equal (Sn-Fe=1.941(3) Å and Fe-O=2.112(3) Å), whereas there are two values of angles (Fe-Sn-F=90.4(1)° and 89.6(1)°; O-Fe-O=91.1(1)° and 88.9(1)°). The material is an ionic compound [SnF₆]^2–[Fe(H₂O)₆]²⁺.     

Mössbauer effect study of the magnetic structure in δ-FeOOH

Two samples of-FeOOH with different particle sizes have been studied in an external field of 4 T and as a function of temperature. They were found to have a ferrimagnetic structure due to an unequal occupancy of antiferromagnetically coupled octahedral ferric ions. The large surface contribution, which is characterized by a canted spin structure and by highly deformed Fe³⁺ co-ordinations, strongly influences the magnetic properties observed with Mössbauer spectroscopy.     

The role of Sb(5+) in the structure of Sb(2)O(3)-B(2)O(3) binary glasses--an NMR and Mössbauer spectroscopy study

Glasses of general formula xSb₂O₃ (1−x)B₂O₃ (0x0.8) have been prepared by conventional melt- quenching. Mössbauer spectroscopy shows that a fraction of the Sb³⁺ is converted to Sb⁵⁺ and this fraction increases with x. High-field ¹¹B MAS NMR gives well-resolved resonances from boron atoms which are 3- and 4-coordinated to oxygen. The fraction of 4-coordinated boron, N₄, goes through a maximum value of 0.12±0.01 at x=0.5. The position of the maximum in N₄ is consistent with the cation potential for Sb³⁺, as observed for other systems. However, the low value of N₄ at this maximum is not so readily explained. The values are similar to those predicted if [BO₄]⁻ were stabilised by [SbO₄]⁺ but the trends with composition are different.     

The proton magnetic resonance study of the structure of Na2Zn(SO4)2·4H2O

The proton magnetic resonance spectra of single crystals of Na₂Zn(SO₄)₂·4H₂O have been investigated and the orientations of the water molecules have been determined. Using the heavy atom structure determined by X-rays a system of hydrogen bonds between water and sulphate oxygens has been proposed.     

Mössbauer studies of the surface and bulk magnetic structure of scandium-substituted Ba-M-type hexaferrites

A direct comparison of the magnetic structures of a surface layer and of the bulk of Ba-M-type hexagonal ferrites with iron ions partially replaced by Sc diamagnetic ions (BaFe_12?x Sc_xO₁₉) has been made by simultaneous Mössbauer spectroscopy with detection of gamma rays, characteristic x-ray emission, and electrons. It has been found that, if the magnetic lattice of a Ba-M-type hexagonal ferrite is weakly diluted by Sc diamagnetic ions, a ～300-nm thick macroscopic layer forms on the surface of a BaFe_11.4Sc_0.6O₁₉ crystal, in which the iron-ion magnetic moments are noncollinear with the moments in the bulk. The noncollinear magnetic structure forms in the near-surface layer of BaFe_12?x Sc_xO₁₉ crystals because the exchange interaction energy is additionally reduced by the presence of such a “defect” as the surface. This is the first observation in ferromagnetic crystals of an anisotropic surface layer whose magnetic properties, as predicted by Néel, differ from those of the bulk.     

Mössbauer study of magnetic order in RBa2Fe3O8

Complete replacement of copper by iron in RBa₂Cu₃O₇ leads to RBa₂Fe₃O₈ (R=Y, rare earth). Mössbauer spectroscopy measurements of⁵⁷Fe and¹⁵¹Eu in RBa₂Fe₃O₈ (R=Y, Eu, Ho, Er) at temperatures 4.2–800 K have been performed. Some of the spectra reveal two inequivalent iron sites, probably corresponding to iron in the Fe(2) site (fivefold oxygen coordination) and in the Fe(1) site (octahedral oxygen coordination). In all compounds the iron moments order antiferromagnetically at the same Néel temperatureT _N720 K. The¹⁵¹Eu Mössbauer spectra of EuBa₂Fe₃O₈ show that the Eu ion is trivalent and exposed to a small exchange field from the iron sublattices.     

High-pressure 155Gd-Mössbauer study of magnetic properties in GdM2 Laves phases (M=Mn,Fe, Al)

Hyperfine Interactions - We report on high-pressure 155Gd-Mössbauer studies of the magnetic properties of GdM2 (Mn, Fe, Al) Laves phases in the cubic C15 phase, and, for the first time, of...     

Mössbauer study of the magnetic high-Tc superconductor GdBa2Cu3O7−δ

The magnetic ordering of the Gd sublattice in superconducting GdBa₂Cu₃O_7-δ is studied by Mössbauer spectroscopy using the 86.5-keV gamma resonance of ¹⁵⁵Gd. Below the Néel temperature of T_N ≌ 2.4 K, the magnetic hyperfine field at the Gd nucleus reflects the increasing local sublattice magnetization extrapolating to a saturation value of B_eff(T=0 K) ≌ 31.5 T. The effective magnetic hyperfine field is found to be parallel to the main axis of the electric-field-gradient tensor, which is characterized by an asymmetry parameter of n = 0.40 ± 0.05. The observed isomer shift and the value of B_eff are typical for trivalent Gd compounds with negligible conduction-electron contributions.     

Magnetic behaviour of γ-Fe2O3 nanoparticles by mössbauer spectroscopy and magnetic measurements

-Fe₂O₃ nanoparticles with varying state of dispersion in a polymer have been investigated by Mössbauer spectroscopy, static magnetic measurements at low applied field, and alternative susceptibility measurements over a large range of frequencies (2×10^–2–10⁴ Hz). The dynamical behaviour was characterized through the variation of the blocking temperature with the characteristic time of the measurement. The Mössbauer blocking temperature was determined according to a procedure described. For quasi-isolated particles an Arrhenius law is demonstrated. Effects of interparticle interactions in concentrated and aggregated systems are satisfactorily explained by the previous model. Dependence of the superparamagnetic susceptibility on the experimental conditions interpreted using the Lorentz or Onsager fields is mentioned.     

Mössbauer and magnetic study of silicon substituted cobalt ferrite

Silicon substituted cobalt ferrites have been investigated for improved performance as stress sensing materials. A series of samples with the formulae CoSi _x Fe_2???x O₄ were prepared using conventional powder ceramic technique. X-ray diffraction patterns were taken to examine spinel crystal structures and energy dispersive spectrometry was done to confirm Si segregations at the grain boundaries. Magnetic and magneto-strictive measurements were carried out to evaluate the material performance. Mössbauer spectra were taken on selective samples to understand the cationic distribution responsible for the modification of properties. The variations are explained on the basis of the strength of the exchange interactions between cations, and anisotropy contributions of cobalt ions. The results demonstrate the possibility of controlling magnetic and magneto-mechanical properties such as Curie temperature and strain derivative through Co and Si substitutions.     

Crystal structure and magnetic properties of Nd（Mn1-xFex）2Si2 compounds

X-ray powder diffraction,resistivity and magnetization studies have been performed on polycrystalline Nd(FexMn1-x)2Si2 (0 ≤ x ≤ 1) compounds which crystallize in a ThCr2Si2-type structure with the space group I4/mmm.The field-cooled temperature dependence of the magnetization curves shows that,at low temperatures,NdFe2Si2 is antiferromagnetic,while the other compounds show ferromagnetic behaviour.The substitution of Fe for Mn leads to a decrease in lattice parameters a,c and unit-cell volume V .The Curie temperature of the compounds first increases,reaches a maximum around x = 0.7,then decreases with Fe content.However,the saturation magnetization decreases monotonically with increasing Fe content.This Fe concentration dependent magnetization of Nd(FexMn1-x)2Si2 compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe.The temperature’s square dependence on electrical resistivity indicates that the curve of Nd(Fe0.6Mn0.4)2Si2 has a quasi-linear character above its Curie temperature,which is typical of simple metals.     

Mössbauer study of the Jahn-Teller effect in Fe0.3Mn2.7O4

The Mössbauer spectra of Fe_0.3Mn_2.7O₄ were investigated in the 288–1473°K temperature range; a tetragonal distortion of the lattice by the Jahn-Teller effect was observed. The results have been compared with point-charge calculations.     

Spatially modulated magnetic structure of AgFeO2: Mössbauer study on 57Fe nuclei

The results of the Mössbauer study of ferrite AgFeO₂ manifesting multiferroic properties (at T ≤ T _N2) have been presented. The hyperfine interaction parameters of ⁵⁷Fe nuclei have been analyzed in a wide temperature range including the points of two magnetic phase transitions (T _N2 ≈ 7–9 K and T _N1 ≈ 15–16 K). It has been shown that the Mössbauer spectra of the ⁵⁷Fe nuclei are sensitive to the variations of the character of the magnetic ordering of Fe³⁺ ions in the studied ferrite. The results of the model identification of a series of spectra (4.7 K ≤ T ≤ T _N2) under the assumption of the cycloid magnetic structure of ferrite AgFeO₂ have been presented. The analysis of the results has been performed in comparison with the literature data for other oxide multiferroics.     

125Te Mössbauer effect study of magnetic hyperfine structure in the ferromagnetic spinel CuCr2Te4

The Mössbauer hyperfine spectrum of ¹²⁵Te has been measured in the ferromagnetic spinel CuCr₂Te₄. The hyperfine field was found to be 148 ± 5 kOe. The nuclear magnetic moment of the 35.6 keV excited state of ¹²⁵Te was determined to be +0.74 ± 0.07 nm.     

Mössbauer studies and magnetic properties of Ln2SrCu2O6 compounds

Mössbauer and magnetic susceptibility measurements were used to study the magnetic properties of Ln_1.9Sr_1.1Cu₂O₆ (Ln=Pr,Nd) and La₂SrCu₂O₆ materials. These compounds were prepared by solid-state reaction and crystallize in a tetragonal structure, space group I4/mmm with two formula units per unit cell. There is only one crystallographic site for Cu atoms, which form a double layer of CuO₅ pyramids. These compounds are not superconducting, but we show, using Mössbauer spectroscopy (MS) on iron doped samples and susceptibility measurements, that the Cu planes order antiferromagnetically. The hyperfine fields on iron nuclei at 4.2 K extend from 472 kOe for La₂SrCu₂O₆ to 501 kOe for Nd_1.9Sr_1.1Cu₂O₆. The ordering temperaturesT _N are: R20, 190, and 250 K for Ln=La, Pr and Nd, respectively.     

Crystal and magnetic properties of the new copper-sodium borate CuNaB3O6 · 0.842H2O

A new compound CuNaB₃O₆ · 0.842H₂O was grown for the first time. Its crystal structure, magnetic susceptibility, and magnetic resonance properties are presented. It was proposed that CuNaB₃O₆ · 0.842H₂O is a spin-Peierls magnet with the transition temperature T _SP ～ 128 K and a ladder spin structure. The possibility of a structural phase transition at T < T _SP is predicted.     

Mössbauer study of proton radiation effects in FeCl24H2O

Abstract

The proton radiation effects in ferrous chloride are studied by means of the Mössbauer spectroscopy. The irradiation with protons of energy of 0.68 to 1.5 MeV has been found to cause dehydration and chemical decomposition of ferrous chloride. FeCl_{2 ·} 2H₂O, and Fe₃O₄ in superparamagnetic and ferromagnetic states, as well as Fe_1?x O were formed. The formation of a superparamagnetic phase of Fe₃O₄ within the “spike” regions was verified by low temperature measurements. The effects observed were interpreted in terms of the “thermal spike” model. The calculated temperatures and radii of “spikes” formed by iron, chloride and oxygen ions are in good agreement with observation for superparamagnetic Fe₃O₄.