Negative tunneling magnetoresistance by canted magnetization in MgO/NiO tunnel barriers

TL;DR

This study demonstrates that canted magnetization in NiO layers causes negative tunneling magnetoresistance in MgO/NiO magnetic tunnel junctions, supported by experimental measurements and theoretical calculations.

Contribution

It reveals the role of non-collinear spin structures in NiO layers as a mechanism for negative TMR in magnetic tunnel junctions.

Findings

Negative TMR of -16% observed at 2.8 K.

Non-collinear spin structures in NiO cause magnetoresistance asymmetry.

Theoretical calculations support experimental results.

Abstract

The influence of insertion of an ultra-thin NiO layer between the MgO barrier and ferromagnetic electrode in magnetic tunnel junctions has been investigated by measuring the tunneling magnetoresistance and the X-ray magnetic circular dichroism (XMCD). The magnetoresistance shows a high asymmetry with respect to bias voltage, giving rise to a negative value of -16% at 2.8 K. We attribute this to the formation of non-collinear spin structures in the NiO layer as observed by XMCD. The magnetic moments of the interface Ni atoms tilt from the easy axis due to exchange interaction and the tilting angle decreases with increasing the NiO thickness. The experimental observations are further support by non-collinear spin density functional theory.