Agneta Seidel

Characterization of rf‐sputtered SnOx thin films by electron microscopy, Hall‐effect measurement, and Mössbauer spectrometry

Characterization of rf-sputtered SnOx films by electron microscopy, Hall-effect measurement and Mossbauer spectrometry

A Mössbauer study of antiferromagnetic ordering in iron deficient TlFe2−xSe2

Abstract TlFe 2- x Se 2 compounds with x values around 0.4 have been characterized by X-ray diffraction and examined by Mossbauer spectroscopy. The iron vacancies are ordered to some extent, but a ThCr 2 Si 2 type subcell structure can be recognized. Antiferromagnetic ordering occurs below a Neel temperature which is strongly dependent on x . The transition seems to be of first order. In contrast to a previous study on a single crystal, these specimens show less pronounced vacancy ordering and a higher extrapolated Neel temperature, which may be explained by a larger number of iron nearest neighbours. The magnetic transition regions are broad, indicating weak interactions between the layers containing iron. A difference in the isomer shifts for the coexisting para- and antiferromagnetic phases was observed, tentatively explained by a difference in the conduction electron density owing to iron vacancies. The electric quadrupole interaction has a T 3 2 dependence in the paramagnetic phase.

Zero-field Mössbauer studies of diferric human transferrin

Diferric transferrin samples labelled with 57Fe at the N- or the C-terminal binding sites are compared by Mössbauer spectroscopy at 15 K and in zero magnetic field. The spectra of the samples are similar but the fitting of single Lorenzian lines to the data shows that some of the line positions differ in the two cases. According to this we can not exclude a difference between the chemical structures of the binding sites that can arise for example from the participation of different forms of the anion and/or water in the two lobes of transferrin. All other line parameters (line-width, intensity) are the same within the limits of errors.

Spin canting and hyperfine interactions in the reentrant Ising spin glass Fe0.62Mn0.38TiO3

The reentrant Ising spin glass Fe0.62Mn0.38TiO3 has been studied with Mossbauer spectroscopy as well as with field-cooled and zero-field-cooled magnetization measurements. The Neel and spin glass temperatures obtained are TN=32.8 K and Tg=25.8 K respectively. The 57Fe Mossbauer spectra recorded below 32 K are described in terms of two subspectra emanating from paramagnetic iron atoms and from iron atoms with canted magnetic moments. The canting angle was determined to be theta approximately=45 degrees for all temperatures below TN. The intensity of the paramagnetic subspectrum decreases with decreasing temperature and is typically about 25% at Tg. Longitudinal as well as transverse reentrant spin glass behaviour is observed in magnetization measurements.

The reentrant Ising Spin Glass Fe0.62Mn0.38TiO3 Studied with the Mössbauer Technique

Abstract The reentrant Ising spin-glass Fe0.62Mn0.38TiO3 has been studied with Mossbauer spectroscopy and SQUID magnetometry. Below the spin-glass freezing temperature of 26.6 K a majority of the iron magnetic moments are canted with respect to the crystallographic c axis. The average canting angle is as large as 〈φ〉 = 41°. There is no abrupt change in 〈φ〉 at the reentrant transition. The probability of the iron magnetic moments to be aligned in the c direction is lower in the spin-glass range than in the antiferromagnetic range. Transversal spin-glass behaviour is observed.

Search for spin canting in gadolinium iron garnet using the Mössbauer technique

We have studied the hyperfine interactions in GdIG in zero external magnetic field using57Fe Mössbauer spectroscopy. Measurements were made at temperatures between 80 K and 310 K, whereby the region around the compensation point at 286 K was emphasized. The easy axis of magnetization was determined to be [111] at all the chosen temperatures. No indications of spin canting were found. The hyperfine parameters vary smoothly with temperature. The temperature dependences of the magnetization of the sublattices are deduced from the magnetic hyperfine fields.

Mössbauer study of the site preference for Fe substitutions in some YBa2Cu3O7-y compounds

YBa2Cu3O7-y compounds with 0.5% of the Cu atoms replaced by 57Fe and with y = 0.15, 0.48, 0.96 and 1.01 have been synthesized. X-ray diffraction showed that the structures are orthorhombic for y < 0.50, tetragonal for larger y and that the volume of the unit cell increases with y. The orthorhombic compounds are superconducting with critical temperatures Tc = 90.7 K and 49 K for y = 0.15 and 0.48 respectively. The tetragonal compounds are semiconducting with band gaps ΔE ≈ 0.15eV for y ≈ 1.0. The Mossbauer spectra give some hints to the site preference of the iron atoms from which we suggest that more than 84% of the Fe atoms substitute for Cu(1) and the rest for Cu(2). Charge states of +3 and +4 for the Fe(2) and the Fe(1) species are consistent with the values of the hyperfine parameters.

A Mössbauer study of the quasi two-dimensional Antiferromagnetic TlFe2-xSe2

TlFe2−xSe2 compounds withx from 0.36 to 0.40 have been examined with Mössbauer spectroscopy. The compounds order antiferromagnetically with broad magnetic transition regions whose width increases with decreasing Fe content. The Néel temperature decreases with x and the temperature variation of the magnetic hyperfine field indicates that the transition is of first order. In samples without vacancy ordering the Fe nuclei experience a different temperature variation of the hyperfine field than in compounds with ordered vacancies.

Mössbauer investigation of 57Fe doped GdBa2Cu3O7-y

We report on Mossbauer spectroscopy of GdBa2(Cu1-x 57Fex)3O7-y superconductors with iron contents x = 0.005, 0.01 and 0.02. The critical temperatures were determined to be Tc = 78, 65 and 56 K respectively for increasing x. Mossbauer spectra were recorded at room temperature and at 5 K. No magnetic ordering appears. All spectra can be analyzed using three quadrupole split doublets whose relative intensities and hyperfine parameters vary with x and with temperature. From the intensities we conclude that roughly 90% of the Fe substitutes for Cu(1) and the rest for Cu(2).

Mössbauer studies of 57Fe-doped CrAs

Abstract A sharp decrease in Neel temperature is observed for a small Fe substitution for Cr in helimagnetic CrAs. The decrease is coupled to a shortening of the crystallographic b -axis. Comparisons of the isomer shifts and electric quadrupole splittings with those for 57 Fe in the other helimagnetic 3d-metal phosphides and arsenides with MnP-type structure are made and differences are explained in terms of nearest metal-nonmetal neighbour distances. The anisotropy of the magnetic hyperfine field for 57 Fe is the smallest among the helimagnetic monopnictides. The main contribution to the hyperfine field comes from the Fermi contact term.