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Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5Br2 revealed by high-field magnetization and 79Br NQR - 125Te NMR
We present high-field magnetization and Br nuclear quadrupole
resonance (NQR) and Te nuclear magnetic resonance (NMR) studies in the
weakly coupled Cu () tetrahedral system CuTeOBr.
The field-induced level crossing effects were observed by the magnetization
measurements in a long-ranged magnetically ordered state which was confirmed by
a strong divergence of the spin-lattice relaxation rate 1/T1 at T0=13.5 K. In
the paramagnetic state, 1/T1 reveals an effective singlet-triplet spin gap much
larger than that observed by static bulk measurements. Our results imply that
the inter- and the intra-tetrahedral interactions compete, but at the same time
they cooperate strengthening effectively the local intratetrahedral exchange
couplings. We discuss that the unusual feature originates from the frustrated
intertetrahedral interactions.Comment: 5 pages, 4 figures, accepted in Phys. Rev. B as a Rapid
Communication
Dynamics of Magnetic Defects in Heavy Fermion LiV2O4 from Stretched Exponential 7Li NMR Relaxation
7Li NMR measurements on LiV2O4 from 0.5 to 4.2 K are reported. A small
concentration of magnetic defects within the structure drastically changes the
7Li nuclear magnetization relaxation versus time from a pure exponential as in
pure LiV2O4 to a stretched exponential, indicating glassy behavior of the
magnetic defects. The stretched exponential function is described as arising
from a distribution of 7Li nuclear spin-lattice relaxation rates and we present
a model for the distribution in terms of the dynamics of the magnetic defects.
Our results explain the origin of recent puzzling 7Li NMR literature data on
LiV2O4 and our model is likely applicable to other glassy systems.Comment: Four typeset pages including four figure
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