The effect of radiofrequency modulation of 57Fe hyperfine interaction by rotating magnetic field

The effect of ⁵⁷Fe hyperfine interaction radiofrequency (rf) modulation by external rotating magnetic field was studied in thin Permalloy foil by means of Mössbauer spectroscopy. The rf effect was investigated as a function of intensity for several rf field frequencies. The experiments show that the external rotating rf field causes considerable changes in the hyperfine pattern. The obtained spectra are in disagreement with those obtained by Perlow [Phys. Rev. 172 (1968) 319]. They also are inconsistent with magnetostriction hypothesis. Proceeding from the Mössbauer spectrum analysis one may conclude that the magnetization of investigated foil changes its direction in a complex manner. However, the undertaken experiments show that the essential number of Mössbauer nuclei experience the rotating magnetic field influence.     

A computer programme for the evaluation of Mössbauer data

A high speed Mössbauer fitting programme of general applicability is described. Its main features are the use of transmission integral procedures, full Hamiltonian diagnonalisation for arbitrary spins, magnetic field distribution analysis to the first order, single or polycrystalline intensity calculation for arbitrary (mixed) transitions, and the option to include Goldanskii-Karyagin or texture effects. The programme is designed to maintain a simple logical structure as seen by the user.     

Double resonance experiments in57Fe Mössbauer spectroscopy

Splitting of Mössbauer lines has been observed in conventional energy domain spectra of Permalloy samples when an external radio frequency (rf) magnetic field was tuned to be in resonance with the separation of Zeeman sublevels of either the ground or the excited state of the⁵⁷Fe nucleus. Time domain measurements were performed with the frequency of the rf field close to the natural linewidth of the 14.4 keV Mössbauer state. A nonmagnetostrictive magnetically soft Permalloy sample was used in the experiments.     

In-beam implantation of iron into germanium in an external magnetic field studied by the Mössbauer effect

In order to determine whether the doublet observed in the Mössbauer spectra of⁵⁷Fe after in-beam, recoil implantation into Ge is due to a quadrupole interaction or corresponds to two implantation sites, this implantation experiment was performed in the presence of a 35 kG external magnetic field. The resulting Mössbauer spectrum favors a dominant quadrupole interaction hypothesis.     

A Mössbauer spectroscopy study of antiferromagnetic iron arachidate Langmuir-Blodgett films

Langmuir-Blodgett multilayers of ferric arachidate (abbreviated: FeA) on silicon wafers have been investigated by means of conversion electron Mössbauer spectroscopy (CEMS) and absorption Mössbauer spectroscopy at different temperatures between room temperature and 4.2 K, without and with external magnetic fields up to 5 T. The films show a quasicrystalline structure with ac-axis orientation perpendicular to the plane and a random distribution of orientations in the plane of the films. All Mössbauer spectra show Fe³⁺. At low temperatures, antiferromagnetic ordering has been observed. The lines in both the room temperature and the low-temperature spectra are significantly broadened, which is due to a distribution of electric field gradients and hyperfine fields. The reason for this is a slightly disordered iron environment. The orientation and the distribution function of the internal magnetic fields have been determined.     

External influence on magnetic properties of Fe-based nanocrystalline alloys

Amorphous and nanocrystalline ribbons of NANOPERM, FINEMET and HITPERM were studied by Mössbauer spectroscopy (MS) after the influence of external factors: different annealing atmospheres, tensile stress and several kinds of corrosion. MS is a suitable tool for such studies because the spectral parameters are very sensitive to changes in the vicinity of the probe — ⁵⁷Fe nuclei. The most sensitive parameters were hyperfine magnetic field in crystalline component, average hyperfine field in amorphous component and direction of net magnetic moments. Influence of external factors modified also the structure of the alloys, i.e. new or modified phases were identified by MS phase analysis.     

Mössbauer diffraction measurements on polycrystalline bcc iron

In the early days of Mössbauer spectroscopy, it was demonstrated that coherent scattering of photons emitted by a Mössbauer source can be observed. In spite of the fact that scattering experiments could give information not accessible by the absorption method, they are not widely used. The reasons for this are, on the one hand, experimental difficulties, and on the other hand, the form of the samples, which should be large single crystals in most cases. In this work, we present a Mössbauer diffraction measurement on polycrystalline bcc iron where these problems have been overcome. We demonstrate that using the kinematical theory of gamma-ray diffraction, useful information on the relative orientation of the crystallographic axis to the hyperfine field directions can be subtracted.     

Application of external magnetic field to characterize magnetic oxides in the carbonaceous chondrite Orgueil

Magnetite is the most common magnetic phase in carbonaceous chondrites. Comprehensive and detailed investigations of this magnetite with X-ray diffraction and electron microprobe have revealed minute amounts of substitutional impurities (e.g. Ni) in the magnetite, but no other magnetic oxides have been found in these meteorites. Using an external magnetic field and Mössbauer spectroscopy, we have found a component in the Mössbauer spectrum that we attribute to maghemite. The relative area of this component implies that maghemite accounts for approximately 12% of the magnetic oxides in Orgueil.     

57Fe and119Sn Mössbauer investigations on some substituted barium hexaferrites

⁵⁷Fe and¹¹⁹Sn Mössbauer measurements have been carried out on powder samples of three differently substituted M-type barium hexaferrites. By⁵⁷Fe Mössbauer measurements in an external magnetic field applied parallel to the -ray direction, we found a canted spin structure for all samples. Furthermore, we detected a strong preference of the Sn⁴⁺ ions for the 4f₂ sites. From⁵⁷Fe Mössbauer measurements aboveT _N, we conclude that the substitution does not influence the 2b sites. The analysis of the magnetically split¹¹⁹Sn Mössbauer spectra at room temperature in the case of the Co-Sn and Zn-Sn substituted samples shows a strong difference between the two. The spectra were interpreted due to the different surroundings of the Sn⁴⁺ ions.     

In-beam Mössbauer spectroscopy on isomer shift and diffusion of interstitial Fe

In-beam Mössbauer spectroscopy (IBMS) is used to study single isolated⁵⁷Fe impurities after implantation in metals and semiconductors with very restricted or even vanishing solubility for Fe. From the Mössbauer parameters it can be inferred that the Fe implants take up substitutional as well as interstitial sites. The strongly increased electron density at the interstitial position in metals is qualitatively explained by the pressure resulting from the small interstitial volume. In Si, Sc and Pb exponential line broadening due to interstitial diffusion has been observed. Additional information on the dynamic behavior and local magnetic structure in some of the systems presented comes from perturbed angular distribution experiments (PAD) performed on an isomeric state of⁵⁴Fe.     

Electron spin relaxation studies of impurity iron ions in ferroelectric lithium niobate

The nuclear hyperfine structure of dilute impurity iron ions in ferroelectric lithium niobate is investigated via⁵⁷Fe Mössbauer effect (ME). The ME spectra exhibit typical slow electron spin relaxation effects associated with Fe³⁺ ions in the⁶S_5/2 state, which are analysed using spin-Hamiltonian formalism. For Fe³⁺ ions, the principal axis of EFG tensor is found to be parallel to the crystallographic c-axis. The strong external magnetic field of 47 KOe is used to study magnetic and crystal field effects on the ME hyperfine structure.     

Maghemite in basalt studied by Mössbauer spectroscopy in external magnetic field

In the present study, we investigate the feasibility of detecting and determining the presence of maghemite in rock samples, by obtaining Mössbauer spectra in an external magnetic field of 1.6 T at room temperature. The interaction of the external magnetic field and the magnetic moments of the sublattices will induce differential shifts in the peak positions. By this method, we can assign some lower limit of the amount of maghemite in the sample. The results are compared with a model for a mixture of maghemite and stoichiometric magnetite.     

Hyperfine interaction of161Dy imprities implated in iron and nickel

In this paper we present a full report on our Mössbauer measurements on implanted sources of¹⁶¹TbFe and¹⁶¹TbNi using the 26.7 keV Mössbauer transition in¹⁶¹Dy. From the measured spectra values were derived for the magnetic and quadrupole interaction strengths of rare earth ions in at least two non-equivalent lattice sites and information is obtained about the relaxation behaviour of these ions.Conclusions are drawn about the lattice location of the implanted ions. Information could also be obtained about the crystalline electric field acting upon the substitutionally implanted rare-earth ions.     

Mössbauer and magnetic studies of orthorhombic FeSiO3

Magnetic properties of orthoferrosilite FeSiO₃ have been examined using susceptibility, magnetization measurements and Mössbauer spectroscopy. From magnetic and Mössbauer measurements, one obtains close values of the magnetic ordering temperature, T_N=39±1 K and T_N=41±1 K, respectively. The magnetic order is characterized by strong ferromagnetic coupling of Fe²⁺ moments within the ribbons and a weak antiferromagnetic coupling of the moments between adjacent ribbons. The 4.2 K Mössbauer spectra can be fitted with two different hyperfine magnetic fields H_hf=68 kOe and H_hf=314 kOe which can be assigned to Fe²⁺ in the octahedrally coordinated M1 and M2 sites, respectively, of the FeSiO₃ structure.     

Step-shape angular spin distribution in layered systems by Fe Mössbauer spectroscopy: A general treatment

In the so-called ‘step-shape’ angular spin distribution model for layered systems, the non-collinear directions of the atomic magnetic moments are confined to the film plane and form a homogeneous fan spanning inside an (in-plane) angular interval Δφ centered at an angle φ₀. A general approach for deriving the two parameters φ₀ and Δφ via ⁵⁷Fe Mössbauer spectroscopy measurements is discussed. The analysis extends our previously reported treatment, which assumed that the angular aperture Δφ develops symmetrically versus a fixed direction φ₀ (e.g., the in-plane easy axis of magnetization) oriented either along or perpendicular to the in-plane projection of the Mössbauer γ-ray direction. The proposed approach is also applicable for those cases when not only the spin aperture Δφ is changing but also the aperture center φ₀ is rotating under the influence of different external parameters, such as applied field, temperature, stress, etc. The method is suitable for applications to nanoscale layered heterostructures with in-plane uniaxial or unidirectional magnetic anisotropy. The method is applied to experimental data obtained on a 2-nm thick defected Fe layer with in-plane magnetic texture.     

Features of the hyperfine interaction of tin impurities in metallic holmium

The Mössbauer effect has been used to study the hyperfine fields for the¹¹⁹Sn atom as an impurity in metallic Ho in the 4.5–136 K temperature range. Two values of the field relevant to the features of the Ho magnetic structure have been found in the ferro- and antiferromagnetic regions of ordering. The temperature dependence of the fields differs drastically from the magnetization function and is similar to the case of a Dy host studied earlier. The experiments with a 40 kOe external magnetic field at 25 K have revealed a strong (up to 19%) hysteresis in the hyperfine fields which can be explained by a rearrangement of the magnetic structure. The field sign has been found to be negative, from which fact a peculiar compensation of the local and hyperfine fields is deduced. The experiment is also indicative of a possible new phase transition at 95 K.     

Magnetic ordering in FexMg1−xCl2, (x=0.55, x=0.45, x=0.30)

Mössbauer measurements on the diluted crystals Fe_xMg_1–xCl₂ show that fluctuating magnetic clusters are present. These can be related to the known spin-glass properties of these compounds. The fluctuating frequencies depend on temperature and the fluctuations can be suppressed by a sufficiently high external magnetic field     

General cases of the pseudoquadrupole interaction in169Tm

Clauser and Mössbauer [1] showed that the second order (in perturbation theory) magnetic hyperfine interaction, the so called pseudoquadrupole inter-action, in the¹⁶⁹Tm Mössbauer effect can produce apparent isomer shifts. While they assumed two isolated singlets and simplified the coupling, we will show that the second order magnetic hyperfine coupling can be observed in general for any kind of crystalline electric field (CEF) wavefunctions, and that the coupling between many states must often be considered in calculating it. Furthermore since the first order magnetic coupling of the excited CEF states is important, the interaction is best accounted for by diagonalization of the full magnetic hyperfine and CEF Hamiltonian. Examples of the effects that may occur are presented.Work supported by the U. S. Department of Energy.     

The influence of the local surrounding on the hyperfine interactions in Zr(Fe1−x Ni x )2 compounds

Mössbauer spectroscopy and the TDPAC method have been used to study Zr(Fe_1–x Ni _x )₂ compounds forx0.30. The hyperfine magnetic field at the Fe sites and the quadrupole splitting as functions of nickel concentration were analysed by use of⁵⁷Fe Mössbauer spectroscopy. Values of the internal magnetic field on¹⁸¹Ta nuclei have been found by means of the TDPAC method.