Skip to main content

2020 03 04 : Condensed Matter Seminar : Topological tunnelling in hybrid magnetic systems

Topological tunnelling in hybrid magnetic systems

  • Date 04 Mar 2020
  • Time 16:00 - 17:00
  • Category Seminar

Dr Matthew Bryan (Dept Electronic Engineering, RHUL)

Magnetic anisotropy is often treated as a uniform property of a material.  This is a reasonable approximation where magnetization structure is dominated by one form of anisotropy.  However, systems with non-uniform anisotropy, such as exchange springs [1] and stress-induced domain wall motion [2], have shown that introducing non-uniformity can lead to novel magnetization behaviour.  This talk will discuss the effects of non-uniform anisotropy in hybrid structures formed by coupling a Permalloy (Ni80Fe20) layer with a Co/Pd stack (treated as a single material layer), which have intrinsically in-plane and out-of-plane anisotropies, respectively.  Due to the different anisotropies, the individual layers favour distinct domain configurations, with the vortex-like Landau pattern preferred in the Permalloy layer and uniform magnetization in the out-of-plane Co/Pd layer.  Coupling the layers results in mutual spin imprinting, in which the magnetization within one layer is imposed on the other.  Depending on the precise layer composition, this can lead to either a pure in-plane Landau domain pattern, an out-of-plane exchange-spring magnetization structure or an anomalous mixed Landau-maze domain state (Fig. 1). 


Topologically, magnetic vortices consist of an in-plane circulating magnetization around a central out-of-plane core, whereas maze domains are formed from oppositely magnetized out-of-plane domains joined by an in-plane domain wall.  Due to the mutual spin imprinting, the vortex core must reside over a like-magnetized maze domain.  Therefore, reversal of vortex core magnetization requires it to cross the in-plane domain wall, conflicting with its out-of-plane topology.  Tunnelling of the vortex core across the domain wall leads to localisation that may benefit low power applications, such as nanoparticle traps, RF oscillators or encryption devices.


Location: Shilling 1-07 (Creative Thinking Room)


Figure 1: Magnetization structure in the mixed Landau-maze domain state within (a) the Co/Pd and (b) the Permalloy layers.


[1] G Asti, et al., Phys. Rev. B, 73, 094406 (2006)

[2] MT Bryan, et al., Phys. Rev. B, 85, 144411 (2012)

2020 03 04 CMSeminar Matthew Bryan

Related topics

Explore Royal Holloway

Get help paying for your studies at Royal Holloway through a range of scholarships and bursaries.

There are lots of exciting ways to get involved at Royal Holloway. Discover new interests and enjoy existing ones

Heading to university is exciting. Finding the right place to live will get you off to a good start

Whether you need support with your health or practical advice on budgeting or finding part-time work, we can help

Discover more about our 21 departments and schools

Find out why Royal Holloway is in the top 25% of UK universities for research rated ‘world-leading’ or ‘internationally excellent’

Royal Holloway is a research intensive university and our academics collaborate across disciplines to achieve excellence.

Discover world-class research at Royal Holloway

Discover more about who we are today, and our vision for the future

Royal Holloway began as two pioneering colleges for the education of women in the 19th century, and their spirit lives on today

We’ve played a role in thousands of careers, some of them particularly remarkable

Find about our decision-making processes and the people who lead and manage Royal Holloway today