111Cd hyperfine probes in YBaCuO

Different techniques like implantation or in-diffusion have been applied to place the hyperfine probe¹¹¹Cd at YBaCuO lattice sites. In this paper different experiments are reviewed which show that the standard PAC-probe can be placed at any regular site of YBaCuO. The PAC-parameters of these sites are collected and discussed. This work was supported by the BMFT, contract: FKZ 13 N 54930     

Hyperfine interaction at111Cd in manganese

The hyperfine interaction is studied in two different crystal lografic forms of Mn. In the -Mn no magnetic, but a distinct electric quadrupole interaction is found. Effects of heat treatment are discussed. For the -Mn two magnetic field sites are found. Their temperature dependence and dependence on the In concentration are discussed.     

PAC study on111Cd in antiferromagnetic CuO

400 keV¹¹¹In⁺ ions were implanted into CuO powder. After annealing at 570 K, more than 50% of the implants were found on substitutional sites in the monoclinic CuO lattice. PAC-spectra taken below the Néel temperatureT _N≈230 K revealed a broadening of the quadrupole spectrum and additional satellite frequencies caused by combined electric and magnetic hyperfine interaction. Assuming that the orientation of the electric field gradient is given by the point charge model and taking the 〈010〉 direction of the supertransferred fieldB _tr in CuO from neutron diffraction, we find a Larmor frequency of ω_L≈40 MHz corresponding toB _tr≈2.7 T at 60 K. Supported in part by BMFT under contract FK213N54930.     

EFG Studies at 111Cd in InBi Systems

TDPAC study of InBi_1−x Te _x with x=0.0, 0.01, 0.05, 0.1 and 0.2 as a function of temperature is done. Both pure and Te-doped samples show a semi-metallic character up to around room temperature. Above room temperature a steep transition to semiconducting state was observed, which is independent of the doping concentrations. Hence Te may be in the interstitial sites. Conductivity measurement of the above samples showed the same trend as observed in the EFG studies. Thus the importance of the conduction electron density is prominently seen in these systems. This revised version was published online in September 2006 with corrections to the Cover Date.     

Quadrupole interaction at111Cd in rare-earth intermetallics

Quadrupole interactions at¹¹¹Cd in various rare-earth intermetallics have been investigated. The enhancement in the efg due to the electronic configurations is found to be small in contrast to pure metals.The authors thank K. Raghunathan for helpful discussions.     

Fluctuating Electric Field Gradients at 111Cd in Ice

¹¹¹Cd–PAC measurements have been made using the high specific activity of ¹¹¹In in the methanol–water mixtures of various concentrations at the room temperature. These experiments revealed that the perturbation factors 〈A ₂ G ₂〉 (integrated over two mean lives τ_N) do not follow the dependence of the macroscopic viscosity η. The observed dynamic character of the PAC spectra in ice is explained by the mobility of orientational and ionic defects. The activation energy for the diffusion process was determined to be E _a =0.35(1) eV. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine interaction of111Cd in In-Pd intermetallic compounds

Perturbed - angular correlation (PAC) spectroscopy was applied to study the hyperfine parameters for¹¹¹In probes in In-Pd intermetallic compounds. The PAC spectra measured in In₃Pd, In₃Pd₂ and InPd₂ compounds reflect the number, population and symmetry of nonequivalent indium probe sites predicted by the crystallographic data. The temperature dependence of the observed electric field gradients was measured in the temperature range 80–873 K.     

Hyperfine interaction of111Cd in antiferromagnetic cobalt oxide

The temperature dependence of the hyperfine field of substitutional¹¹¹Cd in antiferromagnetic CoO has been measured by means of the perturbed angular correlation technique. The Larmor frequency ω_L is found to obey a power law ω_L(t=ω₀ t ^β) up tot _max=0.4 wheret=1−T/T _N is the reduced temperature withT _N=291.2(3) K and β=0.393 (5) the critical exponent. The results are discussed and compared with PAC experiments on¹¹¹Cd in NiO and Ni and with results obtained by other methods.     

Quadrupole interaction at111Cd nuclein in single-crystalline thallium

The quadrupole interaction of¹¹¹Cd nuclei in a single crystal of hexagonal thallium has been investigated for different geometries and sample temperatures employing the perturbed - angular correlation technique. The observed variation of the electric field gradient with temperature is attributed to local modes of thermal vibrations of the Cd impurities. An analytical relationship has been derived from lattice-dynamical models, expressing the temperature dependence in terms of impurity-host mass ratios and local force-constants.     

Phase transitions in the SrHfO3 perovskite measured with 111In/111Cd PAC

The temperature dependence of the hyperfine parameters in SrHfO₃ powder samples has been investigated by means of Perturbed Angular Correlation spectroscopy using implanted ¹¹¹In probes. Three quadrupole interactions have been established, with the largest fraction showing a pronounced dynamic interaction. We assign this fraction to ¹¹¹In / ¹¹¹Cd probe atoms on substitutional Hf sites. The temperature dependence of the dynamic interaction has been associated to the Pnma↔Imma phase transition at ∼700 K. We discuss the results in relation to those obtained for ¹⁸¹Hf / ¹¹¹Ta-probes in AHfO₃ (A=Ba, Sr, Ca) and for ¹¹¹In / ¹¹¹Cd-probes in PbZrO₃ and BaTiO₃. This revised version was published online in August 2006 with corrections to the Cover Date.     

The electric field gradient at111Cd in vanadium oxides

The electric field gradient (efg) of¹¹¹Cd in polycrystalline V₂O₅ was studied using perturbed angular correlation (PAC) spectroscopy, with the¹¹¹In activity ion-implanted at 400 keV. Between the individual steps of an isochronal annealing program, a distinct efg (v _Q 1=88.1(3) MHz, ₁=0.62(2)) was recorded the contribution of which increased with annealing temperature up to 74% at 870 K. Corresponding X-ray analysis of inactive V₂O₅ samples, which underwent the same annealing treatment, proved that the sample always stayed as V₂O₅. Since V₂O₅ has only one equivalent cation site, it is concluded that this efg belongs to¹¹¹Cd at this site. Oxidation of a vanadium foil atT=675 and 800 K at =200 mbar also yielded this efg. From PAC measurements in VO₂, two well-defined efg's were found above and below the metal-semiconductor transition at 340 K, which are tentatively attributed to the monoclinic and the tetragonal phase.Supported by Deutsche Forschungsgemeinschaft and DAAD.On leave from the University of Durban-Westville, South Africa.     

Hyperfine Interaction of 111Cd in Fe3Sn Compound

The hyperfine interaction of ¹¹¹Cd in ferromagnetic Fe₃Sn compound was investigated by TDPAC in the paramagnetic region and below the Curie temperature. The results are compared with hyperfine magnetic fields and EFGs on ¹¹¹Cd and ¹¹⁹Sn in other stoichiometric Fe–Sn phases. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine interactions of111In→111Cd probe atoms on GaAs (111)B reconstructed surfaces

Hyperfine Interactions - We have used111In→111Cd perturbed-angular-correlation (PAC) spectroscopy to measure hyperfine interactions at surface sites on two molecular-beam-epitaxy-grown GaAs...     

111In(111Cd) quadrupole interaction in the chalcogenide spinel CdCr2Se4

The¹¹¹Cd quadrupole coupling in the spinel CdCr₂Se₄ is investigated by TDPAC after different sample treatments. The experiments are consistent with Se vacancies causing the non-cubic probe environments and with the assumption that the majority of the¹¹¹In atoms are positioned at A-sites.