Irreversibility in room temperature current–voltage characteristics of NiFe 2 O 4 nanoparticles: A signature of electrical memory effect P. Dey a,n , Rajesh Debnath b , Swati Singh b , S.K. Mandal b , J.N. Roy a,b a Department of Physics, Kazi Nazrul University, Asansol, W.B. 713340, India b Department of Physics, National Institute of Technology Agartala, Tripura 799046, India article info Article history: Received 15 October 2015 Received in revised form 15 July 2016 Accepted 2 August 2016 Available online 3 August 2016 Keywords: I–V characteristics Electrical irreversibility Hysteresis Nanoparticles NiFe 2 O 4 abstract Room temperature I–V characteristics study, both in presence and absence of magnetic field (1800 Oe), has been performed on NiFe 2 O 4 nanoparticles, having different particle size (Ф14, 21 and 31 nm). Our experiments on these nanoparticles provide evidences for: (1) electrical irreversibility or hysteretic be- haviour; (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 phenom- enon. Interestingly, such effects are found to get reduced with increasing particle size. For NiFe 2 O 4 na- noparticles having Ф¼31 nm, we did not observe any irreversibility effect. This feature has been at- tributed to the enhanced grain surface effect that in turn gives rise to the residual polarization and hence electrical memory effect in NiFe 2 O 4 nanoparticles, having small nanoscopic particle size. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Quest for developing non-volatile memory devices with reli- able data storage, low cost and large area has triggered many re- search groups in the last few years due to its tremendous demand in electronic industries. The digital memory is usually achieved by electrical, optical and magnetic bistable states [1]. Electrical bist- ability is the phenomenon in which a device exhibits two states of different conductivities at same applied voltage. The electrical bistability has been studied through organic/metal/organic layers [2], metal/semiconductor nanoparticles sandwiched between two metallic electrodes [3], granular magnetic tunnel junction [4], or- ganic layer sandwiched between two electrodes [5] etc. In order to realize electrical bistability in hybrid non-volatile memory devices current–voltage (I–V) characteristics is normally studied, where the applied voltage across the device is varied in cycles from po- sitive bias to negative bias and then to positive bias again or vice versa. If there is electrical bistability in the system, then from I–V curves two distinct conducting states, such as high current and low current states are observed. High and low current states cor- respond to ON state and OFF state, respectively. Noteworthy, high conductance state is for random-access memory and low con- ductance state is for read-only memory applications [6]. The so- called “electrical hysteresis”, as obtained from I–V measurement, is an important feature of resistive-switching memory devices [7]. Depending on the nature of I–V curves three modes of non-volatile memory is detected for hybrid system: write-once-read-many- times, unipolar and bipolar electrical switching. Occurrence of ir- reversibility during electrical transition is exhibited by write-once- read-many-times memory on application of external voltage. On the other hand, unipolar and bipolar memories can remember or restore the original conducting state when external voltage is applied to the device with same or different polarity [3]. Till date a lot of research work is going on non-volatile memory devices, starting from thin film [8] to superconducting/ ferromagnetic bi- layers [9] to molecular level [10]. Bandyopadhyay et al. [6] exhibited the conduction switching between multilevel states in I–V plot using Rose Bengal molecules, where two conduction states have been explained by two me- chanisms, namely electro-reduction and conformational change of molecules. Qi et al. [11] has investigated the I–V characteristics of Si nanowires, prepared by metal-assisted chemical etching tech- nique. Ma et al. [2] has fabricated organic/metal/organic tri-layer electrical bistable device, where the I–V characteristic reveals the presence of electrical bistability and also non-volatile memory effect. They have also mentioned that electrical bistability is Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2016.08.004 0304-8853/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: pujaiitkgp2007@gmail.com (P. Dey). Journal of Magnetism and Magnetic Materials 421 (2017) 132–137