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1.
C. Boekema A. B. Denison D. W. Cooke R. H. Heffner R. L. Hutson M. Leon M. E. Schillaci 《Hyperfine Interactions》1983,15(1-4):529-532
Muon Spin Rotation (SR) results for magnetite (Fe3O4) are analyzed and discussed. At room temperature, a SR signal is observed due to the presence of an internal magnetic field (Bint) at the muon site. External transverse field measurements show that Bint is parallel to the magnetic spin direction, the <111> direction in zero applied field. Calculations of the hyperfine field to pinpoint muon stopping sites in magnetite show that the local field contains supertransfer (covalent) and dipolar field contributions. The implanted muons appear to stop at sites structurally similar to those reported for hematite (-Fe3O4), where muon-oxygen bond formation was strongly indicated.Research partially supported by US Department of Energy 相似文献
2.
3.
C. Boekema V. A. M. Brabers R. L. Lichti A. B. Denison D. W. Cooke R. H. Heffner R. L. Hutson M. E. Schillaci D. E. Maclaughlin S. A. Dodds 《Hyperfine Interactions》1986,31(1-4):369-374
Zero-field longitudinal muon-spin-relaxation (μSR) experiments have been performed on single crystals of pseudo-brookite (Fe2−xTil+x
O
5; x=0.25), an anisotropic spin-glass system. The spinglass temperature (Tg) is determined to be 44.0±0.5K. Above Tg, a distinct
exponential muon-spin-relaxation rate (λ) is observed, while below Tg a square-root exponential decay is seen, indicating
fast spin fluctuations in the ‘frozen’ state. Near 8K, a maximum in λ is observed, which is due to transverse spin ordering
at these low temperatures. Even near Tg, λ is very low (<1 μs−1), likely due to a well-defined muon-oxygen state in the single crystals. The sharp λ-increase (with decreasing temperatures)
above Tg allows a comparison between spinfreezing models like the Vogel-Fulcher law and a power law. The results of these
initial measurements indicate that dynamic (and static) magnetism in oxide spin glasses can be directly monitored through
μSR. 相似文献
4.
C. Boekema I. M. Suarez J. C. Lam T. J. Hoffman E. N. La Joie S. F. Weathersby J. A. Flint R. L. Lichti C. P. Wang D. W. Cooke 《Hyperfine Interactions》1991,64(1-4):467-475
Transverse-field (TF) muon-spin-relaxation (μSR) and Mössbauer experiments on the uniaxial insulating spin glass Fe2?xTi1+xO5 (x=0.25) have been performed near and below the spin-glass temperature (T g). The effect of a transverse field on the spin-freezing process and spin-glass state has been investigated by measuring the field-and temperature-dependencies of the μSR parameters. Spin-cluster effects signaled by anomalous μ-spin relaxation have been observed in a temperature region just aboveT g. An interpretation supported by recently developed theoretical models addressing non-linear relaxation in an intermediate Griffiths phase is offered. 相似文献
5.
K. C. B. Chan R. L. Lichti C. Boekema A. B. Denison D. W. Cooke M. E. Schillaci 《Hyperfine Interactions》1986,31(1-4):481-486
A muon site search using calculated internal fields has been performed for V2O3, where purely dipolar fields allow a site determination free from covalent complications. The obtained sites are a subset
of the Rodriguez and Bates sites found in α-Fe2O3 and indicate muon oxygen bond formation. The sites missing at low temperatures are consistent with the vanadium pairing mechanism
for the metal-to-insulator (corundum-to-monoclinic) phase transition. 相似文献
6.
DNA block copolymer doing it all: from selection to self-assembly of semiconducting carbon nanotubes
7.
D. Wayne Cooke Melvin Leon Michael A. Paciotti Peter F. Meier Stephen F. J. Cox Edward A. Davis Thomas L. Estle Bassam Hitti Roger L. Lichti Carolus Boekema John Lam Anny Morrobel-Sosa Jean Oostens 《Hyperfine Interactions》1994,86(1):699-704
A distinctive longitudinal magnetic field dependence of the muon polarization for anomalous muonium in polycrystalline semiconductor targets has been predicted. The polarization exhibits a cusp,i.e., a discontinuous jump in the slope from negative to positive. Measurements of the longitudinal polarization for polycrystalline silicon in fields up to 0.5 T, and temperatures 53 and 200 K have been made at LAMPF. A cusp in the field dependence indeed occurs at 0.345 T, in excellent agreement with the prediction. No cusp is observed at 200 K because Mu* has been thermally ionized. 相似文献
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W. K. Dawson C. H. Halim S. P. Weathersby J. A. Flint J. C. Lam T. J. Hoffman C. Boekema KC. B. Chan R. L. Lichti D. W. Cooke M. S. Jahan J. E. Crow 《Hyperfine Interactions》1991,63(1-4):219-226
Key results of zero-field (ZF) and transverse-field (TF) muon-spin-relaxation (μSR) experiments on superconducting and insulating
RBa2Cu3O
y
(R123
y
, with R=Eu, Gd, Pr and Pr/Y:y=6, 7) are examined. The chemical behavior of the positive muon probe is addressed, and muon-oxygen bonding is shown to occur
in all these cuprates. To explain magnetic fields at muon-probe sites in Pr
x
Y1−x
Ba2Cu3O
y
(0<=x<0.5,y=7 andx=0,y=6) samples, improvements on the reported magnetic structures from neutron diffraction are necessary. Cu magnetism in Pr123y (y=6,7) is observed belowT
N1, which is near RT. The magnetism seen belowT
N2 can be interpreted assuming an additional ordering in the Cutt-O chain layers. Alternatively, Pr ordering is also considered
as the cause of the second phase transition. Considering the specific muon-probe location, a more detailed interpretation
can be provided for the μSR parameters, measured in the normal and mixed states of these unconventional superconductors. 相似文献
10.
M. A. Paciotti D. W. Cooke M. Leon B. L. Bennett C. Pillai O. M. Rivera B. Hitti T. L. Estle S. F. J. Cox R. L. Lichti T. R. Adams C. D. Lamp A. Morrobel-Sosa O. Richter C. Boekema J. Lam S. Alves J. Oostens E. A. Davis 《Hyperfine Interactions》1994,87(1):1111-1116
It has long been recognized thatLCR could profitably be done with the high intensity surface beam at LAMPF [1]. A spectrometer has been built that is matched to the LAMPF beam characteristics. The polarization information is obtained from a downstream array of counters while side counters, containing no polarization signal, monitor the
+ beam. Degraders select higher energy e+, thereby reducing rates and required counter segmentation while maintaining information content. We apply a ramped longitudinal field in addition to the static one to average over instabilities in the
+ beam. This field scan allows direct interpretation of data and does not require a prior estimate of the resonance structure of a sample. Flux coils monitor the applied ramp field and eddy-current induced fields. High average rate (2×107
+/s). good stability, and the versatile field scan permitted useful data to be collected from Cu, Al(Cu), Al, Si(Al), and polycrystalline Si targets. 相似文献