# Magneto-ionic control of spin polarization in magnetic tunnel junctions

## TL;DR

This paper demonstrates large electroresistance and electric control of spin polarization in magnetic tunnel junctions with Hf0.5Zr0.5O2 barriers, highlighting the magneto-ionic effect as the key mechanism.

## Contribution

It reveals the magneto-ionic effect as the origin of large TER and spin polarization control, advancing understanding of electric and magnetic coupling in MTJs.

## Key findings

- TER reaches up to 10^6% under electric cycling
- Electric control of spin polarization with sign reversal of TMR
- Magneto-ionic effect identified as the main mechanism

## Abstract

Magnetic tunnel junctions (MTJs) 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 10^6%. 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.