20 research outputs found
Proposal for a [111] Magnetization Plateau in the Spin Liquid State of Tb2Ti2O7
Despite a Curie-Weiss temperature K, the Tb2Ti2O7
pyrochlore magnetic material lacks long range magnetic order down to at least
mK. It has recently been proposed that the low temperature
collective paramagnetic or spin liquid regime of this material may be akin to a
spin ice state subject to both thermal and quantum fluctuations a {\it
quantum spin ice} (QSI) of sorts. Here we explore the effect of a magnetic
field along the direction on the QSI state. To do so, we
investigate the magnetic properties of a microscopic model of Tb2Ti2O7 in an
independent tetrahedron approximation in a finite along . Such
a model describes semi-quantitatively the collective paramagnetic regime where
nontrivial spin correlations start to develop at the shortest lengthscale, that
is over a single tetrahedron, but where no long range order is yet present. Our
results show that a magnetization plateau develops at low temperatures as the
system develops ferromagnetic spin-ice-like "two-in/two-out"
correlations at the shortest lengthscale. From these results, we are led to
propose that the observation of such a [111] magnetization plateau in Tb2Ti2O7
would provide compelling evidence for a QSI at in this material and
help guide the development of a theory for the origin of its spin liquid state.Comment: 6 pages, 3 figure
Absence of anomalous negative lattice-expansion for polycrystalline sample of Tb2Ti2O7
High resolution X-ray powder-diffraction experiments on a well-characterized
polycrystalline sample of the spin liquid Tb2Ti2O7 reveal that it shows normal
positive thermal-expansion above 4 K, which does not agree with the intriguing
anomalous negative thermal-expansion due to a magneto-elastic coupling reported
for a single crystal sample below 20 K. We also performed a Rietveld profile
refinement of a powder-diffraction pattern taken at a room temperature, and
confirmed that it is consistent with the fully ordered cubic pyrochlore
structure.Comment: 2 pages, 3 figure
The Spin Liquid State of the Tb2Ti2O7 Pyrochlore Antiferromagnet: A Puzzling State of Affairs
The pyrochlore antiferromagnet Tb2Ti2O7 has proven to be an enigma to
experimentalists and theorists working on frustrated magnetic systems. The
experimentally determined energy level structure suggests a local Ising
antiferromagnet at low temperatures, T < 10 K. An appropriate model then
predicts a long-range ordered Q = 0 state below approximately 2 K. However,
muon spin resonance experiments reveal a paramagnetic structure down to tens of
milli-Kelvin. The importance of fluctuations out of the ground state effective
Ising doublet has been recently understood, for the measured paramagnetic
correlations can not be described without including the higher crystal field
states. However, these fluctuations treated within the random phase
approximation (RPA) fail to account for the lack of ordering in this system
below 2 K. In this work, we briefly review the experimental evidence for the
collective paramagnetic state of Tb2Ti2O7. The basic theoretical picture for
this system is discussed, where results from classical spin models are used to
motivate the investigation of quantum effects to lowest order via the RPA.
Avenues for future experimental and theoretical work on Tb2Ti2O7 are presented.Comment: Latex2e,6 pages, IOP format, introduction shortened and other minor
corrections, replaced with published version in the Proceedings of the Highly
Frustrated Magnetism 2003 Conference, Grenobl