# Understanding stability diagram of perpendicular magnetic tunnel junctions

## TL;DR

This paper investigates the stability diagram of perpendicular magnetic tunnel junctions with a focus on optimizing TMR ratio and understanding the interplay of STT, VCMA, and temperature effects in switching behavior.

## Contribution

It introduces an extended stability phase diagram model that incorporates STT, VCMA, and temperature effects, along with independent damping measurements.

## Key findings

- Achieved 180% TMR ratio at room temperature for 1.5 nm CoFeB layer.
- Identified the roles of STT, VCMA, and temperature in switching dynamics.
- Determined STT and VCMA coefficients responsible for magnetization switching.

## Abstract

Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference layer and a composite free layer (FL) are investigated. Different thicknesses of the FL were tested to obtain an optimal balance between tunneling magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier thickness corresponding to the resistance area product RA = 10 Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagrams measured in pillar-shaped MTJs with 130 nm diameter indicate the competition between spin transfer torque (STT), voltage controlled magnetic anisotropy (VCMA) and temperature effects in the switching process. An extended stability phase diagram model that takes into account all three parameters and the effective damping measured independently using broadband ferromagnetic resonance technique enabled the determination of both STT and VCMA coefficients that are responsible for the FL magnetization switching.