Lecturer: Dr. Anna Eyal
Affiliation: Cornell University
Abstract:
The ground states and low temperature
characteristics of frustrated magnetic
systems offer a variety of novel magnetic
states. Among these are the pyrochlore
magnetic insulators Dy2Ti2O7 and
Ho2Ti2O7, for which despite a well-
ordered crystal structure and strong
magnetic interactions between the Dy or
Ho ions, no long-range magnetic order has
been detected [1]. The low-temperature
magnetic state in these materials is
governed by spin-ice rules, in analogy to
water ice. These constrain the Ising-like
spins in the materials, yet does not result
in a global broken symmetry state.
To explore the actual magnetic phases in
these spin-ice materials, we performed
magnetic susceptibility measurements,
employing boundary-free geometries. We
demonstrate a distinctive behavior of the
magnetic susceptibility of both
compounds, that is indistinguishable in
form from the permittivity of supercooled
dipolar liquids. Moreover, we show that
the microscopic magnetic relaxation times
for both materials increase along a super-
Arrhenius trajectory also characteristic of
supercooled glass-forming liquids. Both
materials therefore exhibit characteristics
of a supercooled spin liquid.
Supercooled liquids develop when a solid
does not crystallize upon cooling below its
ordering temperature and, instead, the
microscopic relaxation times diverge so
rapidly that equilibration eventually
becomes impossible. Since supercooled
liquids are glass forming liquids, this
finding indicates the existence of a novel
magnetic glass state in a translationally-
invariant nominally disorder-free
frustrated spin system for the measured
pyrochlores. Differences in the spin
dynamics between the two materials
investigated, specifically in their measured
time scales, are consistent with a strongly-
correlated dynamics of magnetic
monopole excitations. A possible
connection to many-body localization will
also be discussed.
[1] J. S. Gardner, et al., Rev. Mod. Phys.,
82, 53 (2010).