Thermodynamic properties and switching dynamics of perpendicular shape anisotropy MRAM

Wayne Lack*, Sarah Jenkins, Andrea Meo, Roy W. Chantrell, Keith Patrick McKenna, Richard F.L. Evans

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The power consumption of modern random access memory (RAM) has been a motivation for the development of low-power non-volatile magnetic RAM (MRAM). Based on a CoFeB/MgO magnetic tunnel junction, MRAM must satisfy high thermal stability and a low writing current while being scaled down to a sub-20 nm size to compete with the densities of current RAM technology. A recent development has been to exploit perpendicular shape anisotropy along the easy axis by creating tower structures, with the free layers’ thickness (along the easy axis) being larger than its width. Here we use an atomistic model to explore the temperature dependent properties of thin cylindrical MRAM towers of 5 nm diameter while scaling down the free layer from 48 to 8 nm thick. We find thermal fluctuations are a significant driving force for the switching mechanism at operational temperatures by analysing the switching field distribution from hysteresis data. We find that a reduction of the free layer thickness below 18 nm rapidly loses shape anisotropy, and consequently stability, even at 0 K. Additionally, there is a change in the switching mechanism as the free layer is reduced to 8 nm. Coherent rotation is observed for the 8 nm free layer, while all taller towers demonstrate incoherent rotation via a propagated domain wall.

Original languageEnglish
Article number145801
Number of pages15
JournalJournal of Physics Condensed Matter
Issue number14
Publication statusPublished - 5 Jan 2024

Bibliographical note

Funding Information:
The authors gratefully acknowledge the provision of the University of York computing cluster viking. W L acknowledges the support of EPSRC for a PhD studentship.

Publisher Copyright:
© 2024 The Author(s). Published by IOP Publishing Ltd.


  • atomistic
  • magnetism
  • MRAM
  • nanoscale
  • spintronics
  • switching mechanism
  • thermal

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