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  • SOLID-STATE PHYSICS  (9)
  • 1
    Publication Date: 2013-08-31
    Description: The hyperfine field on the muon, B sub hf, at interstitial sites in dilute Fe(Al) alloys was measured for four different concentrations of Al and as a function of temperature by the muon spin rotation method. The magnitude of B sub hf, which is negative, decreases at rates ranging from 0.09 + or - 0.03% per at.% Al at 200 K to an asymptotic limit of 0.35 + or - far above 440 K. This behavior shows that sites near the Al impurity are weakly repulsive to the muon, with an interaction potential of 13 + or - 3 meV. In order to fit the temperature dependence of the hyperfine field, it is necessary to hypothesize the existence of a small concentration of unidentified defects, possibly dislocations, which are attractive to the muon. Although the Al impurity acts as a non-magnetic hole in the Fe lattice, the observed decrease in B sub hf is only 35% of the decrease in the bulk magnetization. It is concluded that B sub hf is determined mainly by the enhanced screening of conduction electrons in Fe and Fe(Al). Since the influence of the Al impurity on the neighboring Fe monents is very small, most of the change in B sub hf is therefore attributed to the increase in conduction electron polarization of the Al impurity.
    Keywords: SOLID-STATE PHYSICS
    Type: NASA-CR-158786
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  • 2
    Publication Date: 2011-08-19
    Description: Nuclear gamma rays in coincidence with outgoing pions and/or protons following single nucleon removal from Mg24 by 200 MeV pi(+) were detected with Ge(Li) detectors. Differential cross sections are reported for gamma rays from the first excited mirror states of Na23 to Mg23 in coincidence with positive pions and/or protons detected in particle telescopes at 30, 60, 90, 120 and 150 deg; angle integrated absolute cross sections and cross section ratios sigma (Mg23/sigma (Na23) are calculated. These results are compared with the predictions of the one step quasifree (OSQF), the intranuclear cascade (INC), and the nucleon charge exchange (NCX) reaction models. The OSQF and the INC calculations generally agree with the experimental results, while the NCX calculations are in disagreement.
    Keywords: SOLID-STATE PHYSICS
    Type: Virginia State Univ. Ativities of the Solid State Physics Research Inst.; 38 p
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  • 3
    Publication Date: 2011-08-19
    Description: Uniaxial stress was used on Fe single crystals to induce muon precession frequency shifts. The frequency shift for a nominally pure Fe sample at 302K was -0.34 + or - .023 MHz per 100 microstrain along the 100 magnetization axis. This corresponds to a change of magnetic field at the muon of 25.1 + to 1.6G/100 magnetic moment. For an Fe (3wt%Si) single crystal the shifts were -0.348 + or - .008 MHz/100 magnetic moment. The agreement between the shifts for Fe and Fe(3wt%Si) shows the effect to be intrinsic to iron and not strongly impurity sensitive. These shifts and their temperature dependence (1/T) are dominated by the effect of strain inducted population shifts between crystallographically equivalent, but mgnetically inequivalent sites. Their magnitudes are in good agreement ith previous theoretical predictions and by previous extrapolation from calculations on Nb and V especially if both 4T(0) and 1T sites contribute comparably.
    Keywords: SOLID-STATE PHYSICS
    Type: Virginia State Univ. Activities of the Solid State Physics Research Inst.; 33 p
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  • 4
    Publication Date: 2013-08-29
    Description: Zero- and longitudinal-field muon spin relaxation measurements on a heavy fermion system CeCu2.1 Si2 have revealed an onset of static magnetic ordering below T(M) approximately 0.8 K, which coexists with superconductivity below T(c) = 0.7 K. The line shapes of the observed muon spin depolarization functions suggest an ordering in either spin glass or incommensurate spin-density-wave state, with a small averaged static moment of the order of 0.1 micro-B per formula unit at T approaches 0.
    Keywords: SOLID-STATE PHYSICS
    Type: Virginia State Univ., Materials Science with Muon Spin Rotation; 14 p
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  • 5
    Publication Date: 2013-08-29
    Description: Zero- and longitudinal-field muon spin relaxation measurements on a polycrystal sample of a heavy fermion superconductor CeCu2.1 Si2 (T(c) = 0.7 K) have revealed an onset of static magnetic ordering below T approximately 0.8 K. The line shapes of the observed spectra in zero field indicate a wide distribution of static random local fields at muon sites, suggesting that the ordering is either spin glass or incommensurate spin-density-wave state. The observed width of the random local field at T = 0.05 K corresponds to a small averaged static moment of the order of 0.1 micro-B per formula unit.
    Keywords: SOLID-STATE PHYSICS
    Type: Virginia State Univ., Materials Science with Muon Spin Rotation; 7 p
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  • 6
    Publication Date: 2013-08-29
    Description: Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La2CuO(4-y) are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.
    Keywords: SOLID-STATE PHYSICS
    Type: Virginia State Univ., Materials Science with Muon Spin Rotation; 10 p
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  • 7
    Publication Date: 2013-08-29
    Description: Motional narrowing of the transverse-field muon spin rotation signal was observed in gamma-TiH(x) for x = 1.83, 1.97, and 1.99. An analysis of the data for TiH1.99 near room temperature indicates that the mechanism responsible for the motion of the muon out of the octahedral site is thermally activated diffusion with an attempt frequency comparable to the optical vibrations of the lattice. Monte Carlo calculations to simulate the effect of muon and proton motion upon the muon field-correlation time were used to interpret the motional narrowing in TiH1.97 near 500 K. The interpretation is dependent upon whether the Bloembergen, Purcell, and Pound (BPP) theory or an independent spin-pair relaxation model is used to obtain the vacancy jump rate from proton NMR T1 measurements. Use of BPP theory shows that the field-correction time can be obtained if the rate of motion of the muon with respect to the rate of the motion for the protons is decreased. An independent spin-pair relaxation model indicates that the field-correlation time can be obtained if the rate of motion for the nearest-neighbor protons is decreased.
    Keywords: SOLID-STATE PHYSICS
    Type: Virginia State Univ., Materials Science with Muon Spin Rotation; 22 p
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  • 8
    Publication Date: 2011-08-18
    Description: The temperature dependence of the interstitial magnetic field, B, as determined by the rotation of the spin of the muon, has been measured for dilute polycrystalline iron alloys with Mo, Ti, and Nb additions over a temperature range of 240 to 633 K. In all cases the behaviors differ from one another and from the Fe(Al) alloys previously studied. B, which is negative with respect to the magnetization, is increased in magnitude by Al and Mo, and decreased greatly by Ti. The addition of Nb creates a two-phase alloy from which the role of heterogeneity and/or strain on B in iron can be assessed. If the temperature dependence of the hyperfine field extracted from B for Fe(Mo) alloys is interpreted on the model previously used to discuss the Fe(Al) data, then the muon must be attracted to the Mo atom while repelled by the Al atoms as the temperature decreases.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Magnetism and Magnetic Materials; 25; 1981
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  • 9
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    In:  CASI
    Publication Date: 2019-07-13
    Description: The muon spin rotation (MuSR) technique is used to probe the microscopic electron density in materials. High temperature MuSR and magnetization measurements in nickel are in progress to allow an unambiguous determination of the muon impurity interaction and the impurity induced change in local spin density. The first results on uniaxial stress induced frequency shifts in an Fe single crystal are also reported.
    Keywords: SOLID-STATE PHYSICS
    Type: NASA-CR-172789 , NAS 1.26:172789
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