437 research outputs found
Ground State of the Easy-Axis Rare-Earth Kagom\'e Langasite PrGaSiO
We report muon spin relaxation (SR) and Ga nuclear quadrupolar
resonance (NQR) local-probe investigations of the kagom\'e compound
PrGaSiO. Small quasi-static random internal fields develop below
40 K and persist down to our base temperature of 21 mK. They originate from
hyperfine-enhanced Pr nuclear magnetism which requires a non-magnetic
Pr crystal-field (CF) ground state. Besides, we observe a broad maximum
of the relaxation rate at K which we attribute to the population of
the first excited magnetic CF level. Our results yield a Van-Vleck paramagnet
picture, at variance with the formerly proposed spin-liquid ground state.Comment: minor change
Ga-NMR local susceptibility of the kagome-based magnet SrCr_9pGa_(12-9p)O_19. A high temperature study
We report a high- Ga-NMR study in the kagome-based antiferromagnetic
compound SrCrGaO (), and present a
refined mean-field analysis of the high T local NMR susceptibility of Cr
frustrated moments. We find that the intralayer kagome coupling is K,
and the interlayer coupling through non-kagome Cr moments is K. The ratio confirms the common belief that
the frustrated entity is a pyrochlore slab.Comment: 8 pages, 4 figures Conference paper: Highly Frustrated Magnetism
2000, Waterloo (Canada) Submitted to Canadian Journal of Physic
Antiferromagnetic correlations and impurity broadening of NMR linewidths in cuprate superconductors
We study a model of a d-wave superconductor with strong potential scatterers
in the presence of antiferromagnetic correlations and apply it to experimental
nuclear magnetic resonance (NMR) results on Zn impurities in the
superconducting state of YBCO. We then focus on the contribution of
impurity-induced paramagnetic moments, with Hubbard correlations in the host
system accounted for in Hartree approximation. We show that local magnetism
around individual impurities broadens the line, but quasiparticle interference
between impurity states plays an important role in smearing out impurity
satellite peaks. The model, together with estimates of vortex lattice effects,
provides a semi-quantitative description of the impurity concentration
dependence of the NMR line shape in the superconducting state, and gives a
qualitative description of the temperature dependence of the line asymmetry. We
argue that impurity-induced paramagnetism and resonant local density of states
effects are both necessary to explain existing experiments.Comment: 15 pages, 23 figures, submitted to Phys. Rev.
Local Moment Formation in the Superconducting State of a Doped Mott Insulator
A microscopic theory is presented for the local moment formation near a
non-magnetic impurity or a copper defect in high-T_c superconductors. We use a
renormalized meanfield theory of the t-J model for a doped Mott insulator and
study the fully self-consistent, spatially unrestricted solutions of the d-wave
superconducting (SC) state in both the spin S=0 and S=1/2 sectors. We find a
transition from the singlet d-wave SC state to a spin doublet SC state when the
renormalized exchange coupling exceeds a doping dependent critical value. The
induced S=1/2 moment is staggered and localized around the impurity. It arises
from the binding of an S=1/2 nodal quasiparticle excitation to the impurity.
The local density of states spectrum is calculated and connections to NMR and
STM experiments are discussed.Comment: 4 pages, 3 figures, revised version, to be published in Phys. Rev.
Let
17O NMR study of the intrinsic magnetic susceptibility and spin dynamics of the quantum kagome antiferromagnet ZnCu3(OH)6Cl2
We report through 17O NMR, an unambiguous local determination of the
intrinsic kagome lattice spin susceptibility as well as that created around
non-magnetic defects issued from natural Zn/ Cu exchange in the S=1/2 (Cu2+)
herbertsmithite ZnCu3(OH)6Cl2 compound. The issue of a singlet-triplet gap is
addressed. The magnetic response around a defect is found to markedly differ
from that observed in non-frustrated antiferromagnetic materials. Finally, we
discuss our relaxation measurements in the light of Cu and Cl NMR data
[cond-mat 070314] and suggest a flat q-dependence of the excitations.Comment: Accepted for publication in Phys. Rev. Lett., 3 jan. 2008 Figure 1
has been modified to include a two-components fit of the 17O NMR spectru
Normal State Magnetic Properties of Ni and Zn Substituted in YBa_{2}Cu_{3} O_{6+x}: Hole-Doping Dependence
We present SQUID susceptibility data on Zn and Ni substituted
YBa_{2}Cu_{3}O_{6+x}. Cross-checks with NMR yield an unprecedented accuracy in
the estimate of the magnetic susceptibility associated with the substituants,
from the underdoped to the lightly overdoped case. This allows us to determine
the Weiss temperature \theta for YBCO: its value is very small for all hole
dopings n_h. Since in conventional metals, the Kondo temperature,
, magnetic screening effects would not be expected for ; in contrast, increasing n_h produces a reduction of the small moment
induced by Zn^{2+} and a nearly constant effective moment for Ni^{2+}
corresponding to a spin 1/2 rather than to a spin 1.Comment: 4 pages, 5 figures, to be published in Europhysics Letter
Relativistic phase space: dimensional recurrences
We derive recurrence relations between phase space expressions in different
dimensions by confining some of the coordinates to tori or spheres of radius
and taking the limit as . These relations take the form of
mass integrals, associated with extraneous momenta (relative to the lower
dimension), and produce the result in the higher dimension.Comment: 13 pages, Latex, to appear in J Phys
Intrinsic susceptibility and bond defects in the novel 2D frustrated antiferromagnet BaSnZnCrGaO
We present microscopic and macroscopic magnetic properties of the highly
frustrated antiferromagnet BaSnZnCrGaO,
respectively probed with NMR and SQUID experiments. The -variation of the
intrinsic susceptibility of the Cr frustrated kagom\'{e} bilayer,
, displays a maximum around 45 K. The dilution of the magnetic
lattice has been studied in detail for . Novel dilution
independent defects, likely related with magnetic bond disorder, are evidenced
and discussed. We compare our results to SrCrGaO. Both
bond defects and spin vacancies do not affect the average susceptibility of the
kagom\'{e} bilayers.Comment: Published in Phys. Rev. Lett. 92, 217202 (2004). Only minor changes
as compared to previous version. 4 pages, 4 figure
Low-energy spin dynamics of the s = 1/2 kagome system herbertsmithite
The low-energy (epsilon = (h) over bar < 1 meV), low-temperature (T = 0.05 K) spin dynamics of the s = 1/2 kagome candidate herbertsmithite are probed in the presence of magnetic fields up to 2.5 T. The zero-field spectra reveal a very weak continuum of scattering at T = 10 K and a broad inelastic peak centred at epsilon(max) = 0.2 meV at lower temperatures, T < 1 K. The broad peak is found to be strongly damped, with a liquid-like structure factor implying correlations at length scales up to r = 6 angstrom. The field dependence of the peak appears to follow the Zeeman splitting of s = 1/2 excitations, consistent with the weakly split 'doublets' observed in low-temperature specific heat. A possible explanation of these observations is a short-range correlated state involving defect spins between the kagome planes and moments in the kagome layers
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