  Out-of-equilibrium investigation of strongly correlated materials deciphers
the hidden equilibrium properties. Herein, we have investigated the
out-of-equilibrium magnetic properties of polycrystalline Dy2Ti2O7 and Ho2Ti2O7
spin ices. The experimental results show the emergence of magnetic
field-induced anomalous hysteresis observed only in temperature/magnetic
field-dependent ac susceptibility measurements. The observed memory effect
(anomalous thermomagnetic hysteresis) strongly depends on the driving thermal
and non-thermal variables. Contrary, in the absence of the magnetic field,
dipolar interaction induced Ising paramagnetic to spin ice crossover develops a
liquid-gas transition type hysteresis below 4 K. Unlike field-induced
hysteresis, it shows weak dependency on thermal and non-thermal variables. Due
to the non-colinear spin structure, the applied dc bias magnetic field produces
quench disorder sites in the cooperative Ising spin matrix and suppresses the
spin-phonon coupling. These quench disorders create dynamic spin correlations
governed by quantum fluctuations, having slow spin relaxation and quick decay
times, which additionally contribute to ac susceptibility. The initial
conditions and measurement protocol decide the magnitude and sign of this
dynamical term contributing to ac susceptibility. It has been suggested that
such kind of out-of-equilibrium properties emerge by the cumulative effect of
geometric frustration, disorder, quantum fluctuations, and the cooperative
nature of spin dynamics of these materials.
