Hyperfine interactions in MnAs probed by57Fe

A transmission Mössbauer study of Mn_0.99Fe_0.01As was performed. At the first order transition near room temperature, all hyperfine parameters show abrupt changes. B_hf at the Fe nucleus shows a peculiar temperature variation, with a maximum value of ?1.2 T. This field is very small relative to a field of 22.7 T at the Mn nucleus measured by N. M. R. The hyperfine interactions are explained within the low ? high spin transition model.     

Hyperfine interactions of 57Fe in iron beam modified metals

It has been known for some years that ion bombardment of a material will bring about a redistribution of its constituents. This can take place by a direct recoil process or as a result of collisional relocation within the collision cascade, known as cascade mixing. Alternatively, there are several mechanisms of radiation enhanced diffusion which may occur if the temperature is sufficiently high. The time scales for these processes are very different. Recent developments have led to the exploration and use of these effects in order to introduce atoms from a coating layer into the substrate below by ion bombardment as an alternative to their direct implantation. This review attempts to clarify the physical processes that occur, and to describe some recent applications to contacts on silicon devices, wear resistant surfaces in titanium alloys, and to achieve corrosion resistance in iron and nickel.     

Hyperfine interactions of 57Fe impurity nuclei in TmNiO3 and YbNiO3 nickelates in the range of magnetic and structure phase transitions

Hyperfine interactions of ⁵⁷Fe impurity nuclei are studied by probe Mössbauer spectroscopy in TmNiO₃ and YbNiO₃ perovskite-like nickelates in the ranges of temperature transitions of an insulator (T < T _IM ) ? metal (T > T _IM ) and antiferromagnetic (T < T _N ) ? paramagnetic (T > T _N ). The changing behavior of hyperfine interaction parameters of ⁵⁷Fe nuclei in the ranges of phase transition temperatures (T _IM and T _N ) is analyzed. The results are interpreted in the context of the charge disproportionation of Ni³⁺ cations associated with the electronic localization in monoclinic-distorted nickelates at T < T _IM .     

Local magnetic structure and anomalies of magnetic hyperfine interactions of57Fe and119Sn nuclei in lithium aluminium ferrites

The⁵⁷Fe and¹¹⁹Sn Mossbauer spectra of ordered ferrites Li_0.5Fe_2.5−xAl_xO₄∶Sn for 0.8<x<1.0 (the compensation point region) have been studied. The spin glass type magnetic structure with the spin canting angle depending on temperature and aluminium concentration is established. Anomalies in the temperature dependence of the hyperfine magnetic field at tin nuclei have been found near the compensation point of the ferrites     

Hyperfine interactions on151Eu and57Fe in amorphous EuFe2Si2

The magnetic and quadrupole hyperfine interactions in amorphous EuFe₂Si₂ have been measured using⁵⁷Fe and¹⁵¹Eu Mössbauer spectroscopy. The distributions in the various parameters have been found using the Fourier coefficient method. Novel features of the results are that the Eu charge state (4f occupation number) changes between the crystalline and amorphous phases and that whereas in the crystalline phase neither Eu nor Fe is magnetic, both become so in the amorphous phase.     

Hyperfine interactions in the anisotropic layer compound FeOCl from57Fe Mössbauer studies

The anisotropic layer compound FeOCl has been synthesized by two different techniques to give, respectively, a large single crystal blade-like product (SC) and a polycrystalline powder product (PC), each of which was examined by temperature dependent⁵⁷Fe Mössbauer spectroscopy over the range 4.2≤T≤300 K. In particular, the onset of magnetic ordering on sample cooling (near 90 K) has been studied in detail, in the light of the 2-dimensional ordering of the paramagnetic ion spins in the crystallographica, c plane. The high temperature (～300 K) and low temperature (～4.2 K) Mössbauer parameters for the SC and PC material are identical within experimental error. The persistence in the spectra of the paramagnetic doublet due to h.s. Fe(III) below the magnetic ordering temperature in the PC material is shown to be consistent with the superparamagnetism of small particles in those samples.     

The splitting of hyperfine lines of57Fe nuclei in RF magnetic field

It is shown experimentally, that for Moessbauer nuclei affected by the radio-frequency (RF) magnetic field of sufficient intensity at frequencies corresponding to NMR, splitting of Zeeman sublevels of nuclei and changes in Moessbauer spectral structure occurs. Depending on the frequency of alternating field each spectral line is splitinto (2·Ig,e +1) comporients, Ig,e-being the nuclear spin of ground and excited state, respectively. The intensity of RF components and the energy gap between them are extremely sensitive to the frequency and the intensity of the RF magnetic field.     

Hyperfine structure of 57Fe in minerals from a manganese ore deposit

Investigations based on ⁵⁷Fe Mössbauer spectroscopy and powder X-ray diffraction report the existence of siderite in a manganese ore deposit in the city of Conselheiro Lafaiete, Minas Gerais, Brazil. Mössbauer parameters at 110 K indicated the isomorphous substitution of Fe^2?+? in siderite structure by other cations such as Ca^2?+? and Mg^2?+?, resulting in the distortion of siderite structure. The proposed mechanism suggests the formation of siderite and it is consistent with the process of carbonate formation in reducing environments.     

Hyperfine interactions of aluminum-substituted goethites in external magnetic fields

Six goethite samples α(Fe, Al)OOH prepared by a similar synthetic method but varying in Al substitution from 0 to 31 mole percent, have been examined by Mössbauer spectroscopy at ≌ 4 K in an external field of 6 T. The resulting spectra have been fitted by two methods: first a simplified model consisting of three distributions of magnetic fields (parallel, perpendicular and antiparallel orientations of internal and external field) and second, a model-independent bi-dimensional distribution of both the internal hyperfine field and the orientation angle ? with the external field. Both fitting methods show that the angular distribution of spins is not random in the case of high Al substitution, but canted towards an antiparallel orientation (?>90°).     

Quadrupole interactions at57Fe in titanium metal

The electric field gradient (EFG) at⁵⁷Fe in titanium is measured using Mössbauer spectroscopy in the temperature range 80°–380°K. The value of EFG obtained at room temperature is 0.53(4)×10¹⁷ V/cm². The value of EFG obtained is compared with the conduction electron charge shift model.     

Hyperfine interactions in electrodeposited Fe x Ni1−x alloys

Mössbauer spectroscopy and X-ray diffraction have been used to study a set of Fe _x Ni_1?x samples obtained by electrodeposition onto graphite. The change of the crystalline structure from fcc to bcc was observed for Fe concentrations betweenx=0.57 and 0.69. Changes of the preferred direction of magnetisation of alloys were observed with the increase of Fe contents.     

Local Structure and Magnetic Hyperfine Interactions of 57Fe Probe Nuclei in TlCr0.9557Fe0.05O3

Journal of Experimental and Theoretical Physics - Mössbauer measurements have been performed on nuclei of 57Fe probe atoms in the perovskite-structure of the TlCr0.9557Fe0.05O3 chromite...     

The three-line magnetic hyperfine spectrum of57Fe

Longitudinal magnetization of a⁵⁷Co in iron metal foil source and an iron metal foil absorber in a uniform external magnetic field results in a simple three-line magnetic hyperfine absorption spectrum. Measurement of the spectral splitting as a function of applied magnetic field yields the⁵⁷Fe excited-and ground-state,g-factors.     

Anisotropy of the Hyperfine Field on 57Fe in Pure and Substituted Yttrium Iron Garnet

Using NMR, anisotropy of the hyperfine field on ⁵⁷Fe nuclei was measured in Y₃Fe₅O₁₂ with nonmagnetic, trivalent substitutions on d (Ga³⁺) and a (Y³⁺ - yttrium antisite defect) sites which are occupied by ferric ions in a pure, stoichiometric system. The measurements were performed by the spin-echo method at liquid helium temperature. Thorough analysis of the hyperfine field anisotropy on the ⁵⁷Fe nuclei in an ideal environment and in an environment where one of Fe³⁺ nearest cation neighbours is replaced by the nonmagnetic impurity is given. When the Fe³⁺ on which the NMR is measured is on the a site and the impurity is Ga³⁺(d), the results may be interpreted in terms of the superposition model. On the other hand, the results for Fe³⁺ on the d site and Y³⁺(a) are in clear disagreement with the predictions of this model. This revised version was published online in July 2006 with corrections to the Cover Date.