Title: Common Glass-Forming Spin-Liquid State in the Pyrochlore Magnets Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$,
Abstract: Despite a well-ordered pyrochlore crystal structure and strong magnetic
interactions between the Dy$^{3+}$ or Ho$^{3+}$ ions, no long range magnetic
order has been detected in the pyrochlore titanates Ho$_2$Ti$_2$O$_7$ and
Dy$_2$Ti$_2$O$_7$. To explore the actual magnetic phase formed by cooling these
materials, we measure their magnetization dynamics using toroidal,
boundary-free magnetization transport techniques. We find that the dynamical
magnetic susceptibility of both compounds has the same distinctive
phenomenology, that is indistinguishable in form from that of the dielectric
permittivity of dipolar glass-forming liquids. Moreover, Ho$_2$Ti$_2$O$_7$ and
Dy$_2$Ti$_2$O$_7$ both exhibit microscopic magnetic relaxation times that
increase along the super-Arrhenius trajectories analogous to those observed in
glass-forming dipolar liquids. Thus, upon cooling below about 2K,
Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$ both appear to enter the same magnetic
state exhibiting the characteristics of a glass-forming spin-liquid.