Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

TL;DR

This study compares tunnel magnetoresistance in magnetic tunnel junctions with alumina, magnesia, and composite barriers, revealing differences in TMR ratios and insights into tunneling mechanisms.

Contribution

It introduces composite tunnel barriers and systematically compares their TMR performance to pure alumina and magnesia barriers.

Findings

Magnesia-based junctions achieve higher TMR ratios than alumina.

Composite barriers show intermediate TMR ratios, indicating suppressed coherent tunneling.

Optimal annealing enhances TMR in all barrier types.

Abstract

Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier.