Magneto-ionic control of spin polarization in multiferroic tunnel junctions

Yingfen Wei,Cynthia P Quinteros,Beatriz Noheda,Guillaume Agnus,Sylvia Matzen,Philippe Lecoeur,Thomas Maroutian

doi:10.1038/s41535-019-0201-0

Abstract

Multiferroic tunnel junctions (MFTJs) with Hf0.5Zr0.5O2 barriers are reported to show both tunneling magnetoresistance effect (TMR) and tunneling electroresistance effect (TER), displaying four resistance states by magnetic and electric field switching. Here we show that, under electric field cycling of large enough magnitude, the TER can reach values as large as 106%. Moreover, concomitant with this TER enhancement, the devices develop electrical control of spin polarization, with sign reversal of the TMR effect. Currently, this intermediate state exists for a limited number of cycles and understanding the origin of these phenomena is key to improve its stability. The experiments presented here point to the magneto-ionic effect as the origin of the large TER and strong magneto-electric coupling, showing that ferroelectric polarization switching of the tunnel barrier is not the main contribution.

Highlights

Combining the tunneling magnetoresistance effect (TMR) effect of magnetic tunnel junctions (MTJs) with additional functionalities provided by the tunnel barrier, i.e., using multiferroic[1] or ferroelectric[2,3] layers as barriers, has drawn considerable attention driven by their potential application in multilevel memories
tunneling electroresistance effect (TER) rises from 102% to 106% with a large number of intermediate states, as shown in Fig. 3a–c, corresponding to Fig. 1d–f, bias-dependence of the TMR in the as-grown state for the same device (Fig. 2, inset), and noting that similar curves are obtained in both HRS and low resistance state (LRS) at stage A for different junctions,[31] it is clear that electric field cycling completely changes the control of the spin polarization of the tunneling electrons
The decrease of transition temperature from stage A to C is consistent with an oxygen deficiency at the LSMO interface[38,39,40] that increases with repeated electric field cycling

Summary

INTRODUCTION

Combining the TMR effect (resistance change induced by magnetic field switching) of magnetic tunnel junctions (MTJs) with additional functionalities provided by the tunnel barrier, i.e., using multiferroic[1] or ferroelectric[2,3] layers as barriers, has drawn considerable attention driven by their potential application in multilevel memories. (LSMO) as bottom elecrode.[28,29,30] The large band gap and high resistance of the HZO layer allows to fabricate full devices with extended electrodes for wire bonding, despite the low thickness of the barrier This is not possible with perovskite ferroelectric (FE) tunnel barriers with such small thickness and, so far these devices have been limited to investigation by scanning probes.[31] Four resistance states have been obtained in this type of junctions by both magnetic and electric field switching, but no ME coupling was reported.[31] Here we show that electric field cycling of high enough amplitude induces irreversible changes in the junction, which evolves from a negligible ME coupling state into a large ME coupling state. In the following we discuss the mechanisms that lead to such phenomena

RESULTS

DISCUSSION

METHODS