  In this work, we report direct as well as pulsed electric field-induced
resistivity switching and its relaxation in a multiferroic insulator La2NiMnO6.
At a fixed base temperature (Tb), the dc resistivity switches abruptly from a
high to a low value, which is manifested as an upward jump in the dc current
density (J) when the electric field (E) exceeds a threshold value Eth. The
fractional change in the resistance is as much as 70 % at room temperature for
Eth = 95 V/cm. The Eth increases with lowering Tb and follows the relation
Eth(Tb) = Eth(0)exp[-Tb/T0], as similar to the behavior found in charge density
wave systems. It is shown that the abrupt jump in J vanishes under pulsed
electric fields if the period between pulses is long enough. Surprisingly, a
step-like increase in J also occurs at a fixed dc electric field (Ec) and T =
Tb, above a threshold waiting time (tth). The tth decreases with increasing Ec
and Tb. Simultaneous measurement of surface temperature during the J-E sweep
and temporal studies suggest that conductive channels are created in an
insulating matrix due to the local self heating, and the coalescence of these
channels above a threshold E- field or time causes the observed anomalies in J.
However, the dissipated Joule power (P = Ith2R) at the transition from high to
low resistive state in the sample decreases with lowering temperature, which
suggests that the Joule heating is the consequence of transition from the high
to low resistance state rather than itself a driving force of the non linear
electrical transport. In addition, non linear J-E characteristics is also found
even with a pulsed voltage sweep, which suggests that intrinsic mechanisms
other than self heating is still active in this material.
