347 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
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
Dzyaloshinsky-Moriya interaction in vesignieite: A route to freezing in a quantum kagome antiferromagnet
We report an electron spin resonance investigation of the geometrically
frustrated spin-1/2 kagome antiferromagnet vesignieite,
BaCuVO(OH). Analysis of the line widths and line shifts
indicates the dominance of in-plane Dzyaloshinsky-Moriya anisotropy that is
proposed to suppress strongly quantum spin fluctuations and thus to promote
long-range ordering rather than a spin-liquid state. We also evidence an
enhanced spin-phonon contribution that might originate from a lattice
instability and discuss the origin of a low-temperature mismatch between
intrinsic and bulk susceptibility in terms of local inhomogeneity
Ground state of the Kagome-like S=1/2 antiferromagnet, Volborthite Cu3V2O7(OH)2.2H2O
Volborthite compound is one of the very few realizations of S=1/2 quantum
spins on a highly frustrated kagome-like lattice. Low-T SQUID measurements
reveal a broad magnetic transition below 2K which is further confirmed by a
peak in the 51V nuclear spin relaxation rate (1/T1) at 1.4K0.2K. Through
51V NMR, the ground state (GS) appears to be a mixture of different spin
configurations, among which 20% correspond to a well defined short range order,
possibly of the type. While the freezing involve all
the Cu spins, only 40% of the copper moment is actually frozen which
suggests that quantum fluctuations strongly renormalize the GS.Comment: 4 pages, 4 figures, to appear in PR
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
On evaluation of two-loop self-energy diagram with three propogator
Small momentum expansion of the "sunset" diagram with three different masses
is obtained. Coefficients at powers of are evaluated explicitly in terms
of dilogarithms and elementary functions. Also some power expansions of
"sunset" diagram in terms of different sets of variables are given.Comment: 9 pages, LaTEX, MSU-PHYS-HEP-Lu3/9
Spin dynamics and disorder effects in the S=1/2 kagome Heisenberg spin liquid phase of kapellasite
We report Cl NMR, ESR, SR and specific heat measurements on the
frustrated kagom\'e magnet kapellasite,
CuZn(OH)Cl, where a gapless spin liquid phase is
stabilized by a set of competing exchange interactions. Our measurements
confirm the ferromagnetic character of the nearest-neighbour exchange
interaction and give an energy scale for the competing interactions K. The study of the temperature-dependent ESR lineshift reveals a
moderate symmetric exchange anisotropy term , with %. These
findings validate a posteriori the use of the Heisenberg
model to describe the magnetic properties of kapellasite [Bernu et al., Phys.
Rev. B 87, 155107 (2013)]. We further confirm that the main deviation from this
model is the severe random depletion of the magnetic kagom\'e lattice by 27%,
due to Cu/Zn site mixing, and specifically address the effect of this disorder
by Cl NMR, performed on an oriented polycrystalline sample.
Surprisingly, while being very sensitive to local structural deformations, our
NMR measurements demonstrate that the system remains homogeneous with a unique
spin susceptibility at high temperature, despite a variety of magnetic
environments. Unconventional spin dynamics is further revealed by NMR and
SR in the low-, correlated, spin liquid regime, where a broad
distribution of spin-lattice relaxation times is observed. We ascribe this to
the presence of local low-energy modes.Comment: 15 pages, 11 figures. To appear in Phys. Rev.
Easy-Axis Kagom\'e Antiferromagnet: Local-Probe Study of NdGaSiO
We report a local-probe investigation of the magnetically anisotropic
kagom\'e compound NdGaSiO. Our zero-field SR results
provide a direct evidence of a fluctuating collective paramagnetic state down
to 60 mK, supported by a wipe-out of the Ga nuclear magnetic resonance (NMR)
signal below 25 K. At 60 mK a dynamics crossover to a much more static state is
observed by SR in magnetic fields above 0.5 T. Accordingly, the NMR signal
is recovered at low above a threshold field, revealing a rapid temperature
and field variation of the magnetic fluctuations.Comment: 4 pages, 4 figure
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