200 research outputs found
Expansion of the Vortex Cores in YBa2Cu3O6.95 at Low Magnetic Fields
Muon spin rotation spectroscopy has been used to measure the effective size
of the vortex cores in optimally doped YBa2Cu3O6.95 as a function of
temperature and magnetic field deep in the superconducting state. While the
core size at H=2T is close to 20 angstroms and consistent with that measured by
STM at 6T, we find a striking increase in the core size at lower magnetic
fields, where it approaches an extraordinarily large value of about 100
angstroms. This suggests that the average value of the superconducting
coherence length in cuprate superconductors may be larger than previously
thought at low magnetic fields.Comment: 9 pages, 4 figures, 1 text fil
Persistent Spin Dynamics in the V Molecular Nano-Magnet
We present muon spin lattice relaxation measurements in the V15 spin 1/2
molecular nano-magnet. We find that the relaxation rate in low magnetic fields
(<5 kG) is temperature independent below ~10 K, implying that the molecular
spin is dynamically fluctuating down to 12 mK. These measurements show that the
fluctuation time increases as the temperature is decreased and saturates at a
value of ~6 nsec at low temperatures. The fluctuations are attributed to V15
molecular spin dynamics perpendicular to the applied magnetic field direction,
induced by coupling between the molecular spin and nuclear spin bath in the
system.Comment: Accepted for publication in Phys. Rev. B, 5 pages, 5 figur
Correlations Between Charge Ordering and Local Magnetic Fields in Overdoped YBaCuO
Zero-field muon spin relaxation (ZF-SR) measurements were undertaken on
under- and overdoped samples of superconducting YBaCuO to
determine the origin of the weak static magnetism recently reported in this
system. The temperature dependence of the muon spin relaxation rate in
overdoped crystals displays an unusual behavior in the superconducting state. A
comparison to the results of NQR and lattice structure experiments on highly
doped samples provides compelling evidence for strong coupling of charge, spin
and structural inhomogeneities.Comment: 4 pages, 4 figures, new data, new figures and modified tex
Hyperfine Fields in an Ag/Fe Multilayer Film Investigated with 8Li beta-Detected Nuclear Magnetic Resonance
Low energy -detected nuclear magnetic resonance (-NMR) was used
to investigate the spatial dependence of the hyperfine magnetic fields induced
by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001)
magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag
layer shows dramatic broadening compared to intrinsic Ag. This broadening is
attributed to large induced magnetic fields in this layer by the magnetic Fe
layer. We find that the induced hyperfine field in the Ag follows a power law
decay away from the Ag/Fe interface with power , and a field
extrapolated to T at the interface.Comment: 5 pages, 4 figure. To be published in Phys. Rev.
-NMR of Isolated Li Implanted into a Thin Copper Film
Depth-controlled -NMR was used to study highly spin-polarized Li
in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive
Knight Shifts and spin relaxation data show that Li occupies two sites at
low temperatures, assigned to be the substitutional () and octahedral ()
interstitial sites. Between 50 to 100 K, there is a site change from to
. The temperature dependence of the Knight shifts and spin-lattice
relaxation rates at high temperatures, i.e. when all the Li are in the
site, is consistent with the Korringa Law for a simple metal.Comment: Accepted for publication in Phys. Rev.
- …