Universality and microstrain origin of the ramp reversal memory effect

The recently discovered ramp reversal memory (RRM) is a nonvolatile memory effect observed in correlated oxides with temperature-driven insulator--metal transitions (IMT). It appears as a resistance increase at predefined temperatures that are set or erased by simple heating--cooling (i.e., ramp reversal) protocols. Until now RRM was measured for two materials: ${\mathrm{VO}}_{2}$ and ${\mathrm{NdNiO}}_{3}$. A heuristic model suggests that the RRM is caused by a local transition temperature increase at boundaries of spatially separated metallic and insulating domains during ramp reversal. However, there is no experimental measure of the magnitude of the effect, which is crucial for the development of a theoretical account of the RRM. Here we show that ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ also shows RRM, including all related features, highlighting the generality of the effect. Moreover, an analysis of the RRM as an effective (average) increase of the critical temperature provides a quantitative measure of its magnitude as a function of temperature and ramp reversal protocols. We provide clear evidence that the RRM is the outcome of a local increase in transition temperature of the microscopic-scale phase boundaries that are created during temperature ramp reversal (from heating to cooling) within the insulator--metal phase coexistence regime.