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Dynamics of muoniated radical states in phthalocyanines
Piroto Duarte, J.; Vilão, R. C.; Alberto, H. V.; Gil, J. M.; Gil, Francisco P. S. C.; Weidinger, A.; Campos, N. Ayres deThis work reports a spectroscopic and spin-dynamics [mu]SR study of the positive muon states formed in the phthalocyanines Zn-Pc, H2-Pc and Cu-Pc. In Zn-Pc and H2-Pc, three distinct muoniated radicals are formed, seen to undergo spin-dynamical processes with charge carriers. Two of the states have very similar hyperfine interaction values, and are believed to be due to muon addition at the outer benzene rings. ...
Muon diffusion and trapping in chalcopyrite semiconductors
Vilão, R. C.; Gil, J. M.; Alberto, H. V.; Duarte, J. Piroto; Campos, N. Ayres de; Weidinger, A.; Yakushev, M. V.; Cox, S. F. J.The diffusion parameters of diamagnetic muons in chalcopyrites CuInSe2, CuInS2, CuInTe2, CuGaTe2 and (Ag0.25Cu0.75)InSe2 were obtained by [mu]SR methods. The variations among the different compositions were found to validate the anion-antibonding localization model. The application of a two-state model to the zero-field data revealed muon trapping by defects. The dipolar width at the trap and the number of jump...
Muon and hydrogen states in II-VI semiconductor compounds. A muSR study
Weidinger, A.; Alberto, H. V.; Gil, J. M.; Vilão, R. C.; Duarte, J. Piroto; Campos, N. Ayres deAdditional hydrogen in II-VI semiconductors may occur in two different configurations, either bound to the anion in a position along the bond direction, or at an open interstitial site surrounded by four cations. The electronic character of these states is very different: the bound hydrogen forms a donor with an extended electronic wave function, whereas the interstitial hydrogen is acceptor-like and has an alm...
Study of Alpha-Sigma Phase Transformation in Mechanically Alloyed Fe-Cr-Sn Alloys
Costa, B.F.O.; Caër, G. Le; Campos, N. Ayres deThe solubility of tin is significantly extended by mechanical alloying in near equiatomic Fe-Cr alloys. The influences of Sn concentration and of grain size on the kinetics of formation of the sigma-phase have been studied using different techniques. The sigma-phase formation is much faster for as-milled alloys than it is for conventional alloys. The sigma-phase formation rate decreases with the increase of Sn ...
Powder Pattern Hyperfine Spectroscopy of Shallow- Donor Muonium Centres
Alberto, H.; Vilão, R.; Duarte, J. Piroto; Gil, J.; Campos, N. Ayres de; Lichti, R.; Davis, E.; Cottrell, S.; Cox, S.Abstract The hyperfine spectroscopy of muonium in II–VI semiconductors is reviewed, suggesting that whereas hydrogen is a deep-level defect in ZnS, ZnSe and ZnTe, it constitutes a shallow donor in ZnO, CdS, CdSe and CdTe. Shallow and deep states coexist in CdTe. Using new data for ZnO, it is shown that the principal values of the muonium hyperfine tensor may be obtained with equal facility from measurements in...
Shallow-level muonium centre in CdS
Gil, J. M.; Alberto, H. V.; Vilão, R. C.; Duarte, J. Piroto; Mendes, P. J.; Campos, N. Ayres de; Weidinger, A.; Krauser, J.; Niedermayer, Ch.A new type of muonium defect centre has been observed in undoped CdS at low temperatures (T<20Â K). The hyperfine parameters are A[short parallel]=335 (7)Â kHz and A[perpendicular]=199 (6)Â kHz (approximately 10-4 of the vacuum value) with the symmetry axis along the Cd-S bond direction. The disappearance of the centre at around 20Â K is in agreement with the binding energy of a shallow centre. The extremely we...
High-temperature trapping of muons in CuInSe2 and CuInS2
Gil, J. M.; Alberto, H. V.; Vilão, R. C.; Duarte, J. Piroto; Mendes, P. J.; Campos, N. Ayres de; Weidinger, A.; Niedermayer, Ch.; Yakushev, M. V.Zero-field [mu]SR measurements were performed at the EMU muon beamline of the ISIS facility on single crystals of p- and n-type CuInSe2 and on crystallites of p-type CuInS2.The diamagnetic centre, thought to be located in all these compounds at the Se anti-bonding interstitial site at low temperatures, is seen to diffuse above 200 K in the Se compound and above 250 K in the S compound. At 380 K the muons are ag...
Study of RFe12−xMox (R =Y, Ho) compounds by neutron powder diffraction, ac susc...
Campos, J. Ayres de; Ferreira, L. P.; Cruz, M. M.; Gil, J. M.; Mendes, P. J.; Ferreira, I. C.; Bacmann, M.; Soubeyroux, J.-L.; Fruchart, D.; Godinho, M.Neutron powder diffraction, magnetization and ac susceptibility measurements were performed on compounds of the series RFe12−xMox (R D Y and Ho, x D 1, 2, 3). The influence of the Mo content on both structural and magnetic properties is discussed. Comparison with published data for different Mo concentrations is made. It is found that the effect of Mo substitution for Fe on structural and magnetic properties ca...
The Secondary Scintillation of Rare Gases under the Influence of Magnetic Fields
Ferreira, M. Fátima A.; Conde, C. A. N.; Campos, N. Ayres de; Gil, J. M. S. C.The influence of magnetic fields on the secondary scintillation of xenon and argon is studied. A small gas cell is used with excitation by alpha-particles and magnetic fields perpendicular to the direction of the electric fields. For reduced electric fields normally used in gas proportional scintillation counters the intensity of the secondary scintillation remains constant, within an accuracy of about ± 1 % fo...
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