Dipolar relaxation and limit of ergodicity in ${\mathrm{K}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Li}}_{\mathrm{x}}$${\mathrm{TaO}}_3$

Evidence is presented for irreversible polarization of ${\mathrm{KTaO}}_3$:Li upon field cycling. In a certain region of field-temperature space, the polarization is also shown to depend on cooling speed. An experimental criterion for nonergodicity is devised to separate the field-temperature space of ${\mathrm{KTaO}}_3$:Li into two regions. The separating line can be fitted to the formula E∼[$T_g$(0)-$T_g$(E${\left)\right]}^{\gamma }$, 1.5≤γ≤2.3. This form was derived from a model postulating a random interaction of infinite range between spins, and independently from a relaxation-time approach involving superparamagnetic moments. While these models are mutually exclusive, we find reasonable coincidence of the data with either of them. From the parameters derived for the respective fits, we conclude, however, that neither of these two models consistently describes all the data presented in ${\mathrm{KTaO}}_3$:Li.