Emergence of field-induced memory effect in spin ices

Abstract: 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.