# Offset fields in perpendicularly magnetized tunnel junctions

## TL;DR

This paper investigates the origin and behavior of offset fields in perpendicularly magnetized tunnel junctions, highlighting how device patterning and stray fields influence these offsets, with implications for MRAM device design.

## Contribution

It provides a detailed analysis of offset fields caused by interlayer exchange and stray fields, offering guidelines for offset field engineering in MRAM devices.

## Key findings

- Offset fields originate from interlayer exchange coupling.
- Patterning alters offset fields due to stray fields.
- Experimental offset fields match spatial averages of stray fields.

## Abstract

We study the offset fields affecting the free layer of perpendicularly magnetized tunnel junctions. In extended films, the free layer offset field results from interlayer exchange coupling with the reference layer through the MgO tunnel oxide. The free layer offset field is thus accompanied with a shift of the free layer and reference layer ferromagnetic resonance frequencies. The shifts depend on the mutual orientation of the two magnetizations. The offset field decreases with the resistance area product of the tunnel oxide. Patterning the tunnel junction into an STT-MRAM disk-shaped cell changes substantially the offset field, as the reduction of the lateral dimension comes with the generation of stray fields by the reference and the hard layer. The experimental offset field compares best with the spatial average of the sum of these stray fields, thereby providing guidelines for the offset field engineering.