Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers

TL;DR

This study investigates the antiferromagnetic coupling in CoFeB/Ru/CoFeB trilayers, revealing oscillatory behavior with Ru thickness and effects of annealing on magnetic properties, relevant for magnetic tunnel junctions.

Contribution

It demonstrates the oscillatory antiferromagnetic coupling in amorphous CoFeB/Ru/CoFeB trilayers and analyzes the effects of annealing on magnetic switching and coupling strength.

Findings

Antiferromagnetic coupling oscillates with Ru thickness, peaking at 1.0-1.1 nm.

Annealing at 350°C reduces coupling and increases coercivity.

High tunneling magnetoresistance (~50%) achieved in device applications.

Abstract

This work reports on the magnetic interlayer coupling between two amorphous CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic coupling which oscillates as a function of the Ru thickness x, with the second antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found that the coercivity depends on the net magnetic moment, i.e. the thickness difference of the two CoFeB layers. The antiferromagnetic coupling is almost independent on the annealing temperatures up to 300 degree C while an annealing at 350 degree C reduces the coupling and increases the coercivity, indicating the onset of crystallization. Used as a soft electrode in a magnetic tunnel junction, a high tunneling magnetoresistance of about 50%, a well defined plateau and a rectangular switching behavior is achieved.