Irreversibility in room temperature current-voltage characteristics of NiFe2O4 nanoparticles: A signature of electrical memory effect

Room temperature I-V characteristics study, both in presence and absence of magnetic field (1800 Oe), has been performed on NiFe2O4 nanoparticles, having different particle size (Ф~14, 21 and 31 nm). Our experiments on these nanoparticles provide evidences for: (1) electrical irreversibility or hysteretic behaviour; (2) positive magnetoresistance and (3) magnetic field dependent electrical irreversibility or hysteresis in the sample. “Hysteretic” nature of I-V curve reveals the existence of electrical memory effect in the sample. Significantly, such hysteresis has been found to be tuned by magnetic field. In order to explain the observed electrical irreversibility, we have proposed a phenomenological model on the light of induced polarization in the sample. Both the positive magnetoresistance and the observed magnetic field dependence of electrical irreversibility have been explained through magnetostriction phenomenon. Interestingly, such effects are found to get reduced with increasing particle size. For NiFe2O4 nanoparticles having Ф=31 nm, we did not observe any irreversibility effect. This feature has been attributed to the enhanced grain surface effect that in turn gives rise to the residual polarization and hence electrical memory effect in NiFe2O4 nanoparticles, having small nanoscopic particle size.