R. Wäppling

Muon diffusion and trapping in proton conducting oxides

Abstract Trapping as a main feature of proton diffusion in proton conducting oxides was investigated by means of muon spin relaxation measurements, with the positive muon as tracer. In Sc-doped SrZrO 3 , a system with representative physico-chemical properties and favourable nuclear magnetic moments, the muons are trapped at single Sc ions at a distance of 2.49 A with a binding energy of 0.2 eV, in accordance with previous proton results. The muons form muoxide ions which are directed along the bisector of two oxygen–oxygen connection lines. The μSR spectra could quantitatively be described in terms of a two-state model for the muon diffusion comprising random sequences of trapping events and free diffusion periods.

Mössbauer Study of Ordering in FeSi Alloys

The ordering in FeSi alloys with Si-content less than 25 at% has been examined. At low Si contents there is a relatively strong preference for large Si-Si inter-atomic distances. Furthermore a two phase region exists in the region from about 10 at% to about 20 at% Si, one of the phases probably of DO3 type.

First order magnetic transition, magnetic structure, and vacancy distribution in Fe2P

Abstract The para- to ferromagnetic transition in Fe 2 P has been studied using Mossbauer spectroscopy. The magnetic hyperfine fields drop abruptly from about half of their saturation values to zero at 214.5 K indicating a first order transition. The isomer shifts show a discontinuous change at the transition point. For some samples the transition takes place over a wide temperature range, probably due to impurities and other imperfections in the samples. From the magnetic hyperfine fields at 15 K the magnetic moments can be deduced to be 1.14 μ B and 1.78 μ B for Fe(1) and Fe(2), respectively. An assignment of the components in the Mossbauer spectra to the two crystallographically nonequivalent iron positions has been made from the temperature variation of the spectra. The ordering of metal vacancies has been investigated by a Mossbauer study of a nonstoichiometric Fe 2 P sample and by an X-ray diffraction study of a nonstoichiometric Mn 2 P crystal.

Mössbauer study of phosphides containing iron

Abstract A series of binary and ternary transition metal phosphides containing iron has been investigated by Mossbauer spectroscopy. Most of the compounds studied show complex magnetic behaviour, and interpretations are proposed for some cases. The crystallographic ordering mechanism in Me 2 P-type phosphides is discussed, and it is shown that great care must be taken in assigning the observed components of the Mossbauer spectra to the various crystallographic positions of the iron atoms.

Magnetic properties of two-dimensional arrays of epitaxial Fe (001) submicron particles

The magnetic properties of two-dimensional arrays of Fe particles with well-defined geometry, prepared by electron lithography from epitaxial Fe (001) films of thickness of 50 nm, have been studied. Circular particles with diameters of 0.6 and 0.4 m and rectangular particles 0.9 m0.3 m and 0.7 m0.2 m, were positioned in square and rectangular lattices, respectively, with lattice constants about twice the particle dimensions. Samples were prepared with the lattices oriented along the 100 and 110 directions. Hysteresis curves were obtained in the field range 2 T at temperatures between 30 and 300 K. The hysteresis curves are characteristic for single particles with a multidomain zero-field state. The magnetization and demagnetization processes are mainly governed by the geometrical shape of the particles and their orientation with respect to the crystal directions and the applied field. This implies that the high quality in the epitaxial Fe films is preserved during the patterning process. Magnetic images, obtained by magnetic force microscopy, support the conclusions drawn from the magnetization measurements. The circular particles showed a fourfold symmetry in their magnetic image, which is compatible with the expected domain structure in a disk with cubic crystalline anisotropy

The positive muon in the intermetallic hydride ZrV2Hx: A muon tracer study supplemented by differential thermoanalysis, neutron vibrational spectroscopy, and quasielastic neutron scattering

ZrV2 is an intermetallic compound with energetically different interstitial sites, which upon hydrogenation are successively filled with hydrogen (thermodynamic distribution). When a positive muon is added as a microscopic probe, it is thermalized at random and thus at low temperatures statistically distributed over the available (unblocked) interstices. By varying the preloading we scan the accessible hydrogen sites and find that at high hydrogen content three kinds of interstices are occupied, in contradiction to literature diffraction data. This surprising result is confirmed by a detailed neutron vibrational spectroscopy study on ZrV2Hx which is presented as well. The temperature dependence of the μ+ relaxation rate is textbook‐like in empty ZrV2: static muon at T 200 K. In ZrV2Hx, however, the relaxation rate exhibits an intermediate plateau which we attribute to a relocation of the muon. The motion of the muon above 150 K is interpreted as being directly relate...

A mu SR study of paramagnetic fluctuations in rare-earth-aluminium intermetallics

The authors have studied magnetic fluctuations in the paramagnetic phase of rare-earth-aluminium intermetallics of the type (RE)Al2 by the method of transverse-field muon spin rotation ( mu SR). In the case with strong 4f exchange they could observe a strong increase in the damping of the mu SR signal on approaching the Curie point Tc. One important contribution to the increased damping rate is the slowing down of magnetic fluctuations attributed to the formation of paramagnetic spin correlations which are observed to persist far above Tc. The crystallographic site for the mu + is discussed as well as the hyperfine field induced at this site due to interstitial electron polarisation.

Mössbauer determination of the E2/M1 mixing ratio of the 77 keV transition in197Au and of the sign of the electric field gradient in KAu(CN)2

A Mössbauer measurement of the E2/M1 mixing ratio of the 77 KeV transition in197Au yielded δ=−0.352±0.005. With this result, Mössbauer absorption spectra of KAu(CN)2 single crystals show that the electric field gradient at197Au in this compound is negative. This implies that the field gradient is mainly produced by 6pz electrons. The data also indicate a large vibrational anisotropy of Au in KAu(CN)2.

Studies of the Magnetic Structure of FeSn Using the Mössbauer Effect

From the analysis of 57Fe and 119Sn Mossbauer spectra a modified anti-ferromagnetic spin structure is proposed. The ferromagnetic ordering of the iron moments in the basal planes is partly destroyed and the magnetic unit cell is four times as large as the chemical unit cell, being doubled both along the a and the c axis. The temperature variation of the reduced magnetic hyperfine field for Sn(1) strongly deviates from the corresponding quantity found for iron. The Neel temperature is found to be 368 K and the critical exponent β obtained is 0.340.

Mössbauer study of iron-rich biotites

It has been possible by detailed studies of the Mossbauer spectra for biotite, to distinguish between the two iron sites.