LIGAND FIELD CALCULATION FOR THE COMPLEX Fe(H2O)2+6 IN FROZEN AQUEOUS SOLUTION OF Fe(ClO4)2

Switching Reciprocity On and Off in a Magneto-Optical X-Ray Scattering Experiment Using Nuclear Resonance of 57Fe Foils

Reciprocity is when the scattering amplitude of wave propagation satisfies a symmetry property, connecting a scattering process with an appropriate reversed one. We report on an experiment using nuclear resonance scattering of synchrotron radiation, which demonstrates that magneto-optical materials do not necessarily violate reciprocity. The setting enables to switch easily between reciprocity and its violation. In the latter case, the exhibited reciprocity violation is orders of magnitude larger than achieved by previous wave scattering experiments.

A common optical algorithm for the evaluation of specular spin polarized neutron and Mössbauer reflectivities

Using the general approach of Lax for multiple scattering of waves a 2x2 covariant expression for the reflectivity of polarized slow neutrons of a magnetic layer structure of arbitrary complexity is given including polarization effects of the external magnetic field. The present formalism is identical to the earlier published one for the (nuclear) resonant X-ray (Mossbauer) reflectivity and properly takes the effect of the external magnetic field of arbitrary direction on the neutron beam into account. The form of the reflectivity matrix allows for an efficient numerical calculation.

Switching Reciprocity On and Off in a Magneto-Optical X-Ray Scattering Experiment Using Nuclear Resonance ofα−Fe57Foils

Reciprocity is when the scattering amplitude of wave propagation satisfies a symmetry property, connecting a scattering process with an appropriate reversed one. We report on an experiment using nuclear resonance scattering of synchrotron radiation, which demonstrates that magneto-optical materials do not necessarily violate reciprocity. The setting enables us to switch easily between reciprocity and its violation. In the latter case, the exhibited reciprocity violation is orders of magnitude larger than achieved by previous wave scattering experiments.

57Co emission studies of cupric oxide

Results on the incorporation, valence and spin states of Fe(Co) in CuO (with reference to similar studies on high temperature superconductors) and coupling of the Fe(Co) moment to the Cu magnetism in CuO are presented. Freshly prepared57Co: CuO shows two quadrupole doublets D1 and D2 withQ.S. of 2.49 and 1.52,I.S. of 0.35 and 0.70 mm/s and relative abundance of 74% and 26%, respectively at room temperature, the abundance being dependent on time in a sample exposed to ambient conditions and reaching 38 to 62% fifteen months after preparation. Below,TN=2251K, a typical combined magnetic-quadrupole interaction pattern is observed with a single saturation magnetic hfs of 25.6 T, central shift o…

Icems and dcems study of Fe layers evaporated onto Al and Si

Thin layers of57Fe (2.5 nm, 10 nm and 70 nm thickness), vacuum evaporated onto Al and Si plates, have been investigated by conversion electron Mossbauer spectroscopy (CEMS). The measurements were performed employing both a proportional counter and a channeltron for conventional and ultrahigh-vacuum integral CEMS (UHV-ICEMS) studies, respectively, and a channeltron for depth-selective CEMS (DCEMS). The phase analysis of the layers on base of experimental results has indicated the presence of metallic iron and one or two iron compounds, ascribed to iron reaction products formed with the residual gas during evaporation. These products are most likely rather stable iron nitrides, are more or le…

Coarsening of Antiferromagnetic Domains in Multilayers: The Key Role of Magnetocrystalline Anisotropy

The domain structure of an antiferromagnetic superlattice is studied. Synchrotron Mössbauer and polarized neutron reflectometric maps show micrometer-size primary domain formation as the external field decreases from saturation to remanence. A secondary domain state consisting mainly of at least 1 order of magnitude larger domains is created when a small field along the layer magnetizations induces a bulk-spin-flop transition. The domain-size distribution is reproducibly dependent on the magnetic prehistory. The condition for domain coarsening is shown to be the equilibrium of the external field energy with the anisotropy energy.

Comparative Mössbauer spectroscopic study of iron impurities in ZnSe

Abstract An anomalous spectral doublet attributed to Fe 2+ impurity pairs is observed in Mossbauer absorption spectra of 57 Fe 0.01 Zn 0.99 Se below room temperature. In Mossbauer emission experiments, ZnSe: 57 Co polycrystal and powder sources exhibit below 45 K the nucleogenic Fe 1+ valence state born as an after effect of the electron-capture decay of 57 Co. Above 8 K, the proportion of the nucleogenic Fe 1+ decreases under the effect of the thermally activated Fe 1+ →Fe 2+ relaxation. The activation energy is estimated to 0.004 eV. While nucleogenic Fe 1+ is absent in ZnSe: 57 Co single crystal spectra, increasing proportions are detected in samples with an enhanced specific surface. Th…

Coherent forward-scattering amplitude in transmission and grazing incidence Mössbauer spectroscopy

The theory of both transmission and grazing incidence M\"ossbauer spectroscopy is re-analyzed. Starting with the nuclear susceptibility tensor a common concise first order perturbation formulation is given by introducing the forward scattering amplitude into an anisotropic optical scheme. Formulae of Blume and Kistner as well as those of Andreeva are re-derived for the forward scattering and grazing incidence geometries, respectively. Limitations of several previously intuitively introduced approximations are pointed out. The grazing incidence integral propagation matrices are written in a form built up from 2x2 matrix exponentials which is particularly suitable for numerical calculations a…

Electron trapping centres and cross sections in LiNbO3studied by57Co Mössbauer emission spectroscopy

Fast electron trapping processes and aliovalent charge states following the 57Co(EC)57Fe decay are studied in undoped, 5.4 mol% Mg-doped and 0.1 mol% Fe-doped LiNbO3 in various thermochemical reduction (TCR) states. Static 57Co Mossbauer emission spectra of congruent Mg:LiNbO3 recorded at T = 4.2 K in external magnetic field of 4.6 T are presented. Trapping cross section ratios are derived for Fe3+Li, Nb5+Li and Mg2+Li. A method to determine trap concentrations for TCR states of LiNbO3 is outlined. The electron-capture distance of the traps is found to be 2.7±1.4 nm. As this is much smaller than the 6 keV Auger-electron penetration depth, it is concluded that the distribution of the alioval…

Poster contributions

Mössbauer Spectroscopic Evidence of Angle-Dependent Intersystem Crossing in LiNbO3:Fe3+

M\"ossbauer emission spectra of LiNb${\mathrm{O}}_{3}$:$^{57}\mathrm{Co}$ single crystals in magnetic fields up to 5 T at 4.2 K show initial populations of the $^{6}A_{1\mathrm{g}}$ Zeeman substates of ${\mathrm{Fe}}^{3+}$ which depend strongly on the angle between the crystallographic $c$ axis and the magnetic field. This is interpreted in terms of a crystal-field effect on excited states which influences the initial populations of the Zeeman sublevels of the $^{6}A_{1\mathrm{g}}$ ground term after the electron-capture decay of $^{57}\mathrm{Co}$. An intersystem crossing process due to orbit-lattice interaction can fairly well explain the angular dependence.

Realizing total reciprocity violation in the phase for photon scattering

Scientific reports 7, 43114 (2017). doi:10.1038/srep43114

Synchrotron Mössbauer Reflectometry in Materials Science

57Fe nuclear resonant scattering experiments are reported on iron-containing thin films using 14.41 keV synchrotron radiation at angles of grazing incidence around and slightly above the critical angle of the electronic total reflection. In partially oxidised α–Fe films of 20 nm original thickness various oxide and oxihydroxide phases are identified at different depth. In a [Fe/FeSi]10multilayer grown on Zerodur®substrate the Fe—Fe interlayer coupling varies with the distance from the substrate. The antiferromagnetic order of the top layers of this multilayer can be suppressed by external magnetic field. These examples demonstrate the efficiency of synchrotron Mossbauer reflectometry (SMR),…