Magnetic polaron imaged for the first time

September 15, 2016
Magnetic polaron imaged for the first time
Electron microscopy image of a small fraction of the dipolar dice lattice. The spin ice structure consists of interacting ferromagnetic nanoislands. The experimental lattice consists of several thousand nanoislands and is fabricated by electron-beam lithography. Credit: Aalto University

Researchers at Aalto University and Lawrence Berkeley National Laboratory have demonstrated that polaron formation also occurs in a system of magnetic charges, and not just in a system of electric charges. Being able to control the transport properties of such charges could enable new devices based on magnetic rather than electric charges, for example computer memories.

Polarons are an example of emergent phenomena known to occur in condensed matter physics. For instance, an electron moving across a crystal lattice displaces the surrounding ions, together creating an effective quasi-particle, a polaron, which has an energy and mass that differs from that of a bare electron. Polarons have a profound effect on electronic transport in materials.

Artificial spin ice systems are metamaterials that consist of lithographically patterned nanomagnets in an ordered two-dimensional geometry. The individual magnetic building blocks of a spin ice lattice interact with each other via dipolar magnetic fields.

Researchers used material design as a tool to create a new artificial spin ice, the dipolar dice lattice.

'Designing the correct two-dimensional lattice geometry made it possible to create and observe the decay of magnetic polarons in real-time,' says postdoctoral researcher Alan Farhan from Lawrence Berkeley National Laboratory (USA).

'We introduced the dipolar dice lattice because it offers a high degree of frustration, meaning that competing magnetic interactions cannot be satisfied simultaneously. Like all systems in nature, the dipolar dice lattice aims to relax and settle into a low-energy state. As a result, whenever magnetic charge excitations emerge over time, they tend to get screened by opposite magnetic charges from the environment,' explains Dr. Farhan.

The researchers at Berkeley used photoemission electron microscopy, or PEEM, to make the observations. This technique images the direction of magnetization in individual nanomagnets. With the magnetic moments thermally fluctuating, the creation and decay of magnetic polarons could be imaged in real space and time. Postdoctoral researcher Charlotte Peterson and Professor Mikko Alava at Aalto University (Finland) performed simulations, which confirmed the rich thermodynamic behavior of the spin ice system.

'The experiments also demonstrate that magnetic excitations can be engineered at will by a clever choice of geometry and the size and shape of individual nanomagnets. Thus, artificial is a prime example of a designer material. Instead of accepting what nature offers, it is now possible to assemble new materials from known building blocks with purposefully designed functionalities,' says Professor Sebastiaan van Dijken from Aalto University.

'This concept, which goes well beyond magnetic metamaterials, is only just emerging and will dramatically shape the frontier of materials research in the next decade,' adds Professor van Dijken.

Explore further: Researchers create 'rewritable magnetic charge ice'

More information: Alan Farhan et al. Thermodynamics of emergent magnetic charge screening in artificial spin ice, Nature Communications (2016). DOI: 10.1038/ncomms12635

Related Stories

Researchers create 'rewritable magnetic charge ice'

May 19, 2016

A team of scientists working at the U.S. Department of Energy's (DOE) Argonne National Laboratory and led by Northern Illinois University physicist and Argonne materials scientist Zhili Xiao has created a new material, called ...

Magnetic charge crystals imaged in artificial spin ice

August 28, 2013

A team of scientists has reported direct visualization of magnetic charge crystallization in an artificial spin ice material, a first in the study of a relatively new class of frustrated artificial magnetic materials-by-design ...

Recommended for you

Gravitational waves may oscillate, just like neutrinos

September 21, 2017

(Phys.org)—Using data from the first-ever gravitational waves detected last year, along with a theoretical analysis, physicists have shown that gravitational waves may oscillate between two different forms called "g" and ...

Detecting cosmic rays from a galaxy far, far away

September 21, 2017

In an article published today in the journal Science, the Pierre Auger Collaboration has definitively answered the question of whether cosmic particles from outside the Milky Way Galaxy. The article, titled "Observation of ...

New technique accurately digitizes transparent objects

September 21, 2017

A new imaging technique makes it possible to precisely digitize clear objects and their surroundings, an achievement that has eluded current state-of-the-art 3D rendering methods. The ability to create detailed, 3D digital ...

Physicists publish new findings on electron emission

September 21, 2017

Even more than 100 years after Einstein's explanation of photoemission the process of electron emission from a solid material upon illumination with light still poses challenging surprises. In the report now published in ...

New analysis explains role of defects in metal oxides

September 21, 2017

Sometimes things that are technically defects, such as imperfections in a material's crystal lattice, can actually produce changes in properties that open up new kinds of useful applications. New research from a team at MIT ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Hyperfuzzy
1 / 5 (1) Sep 15, 2016
Interesting concept; however, concept and reality are two different things. So I have no idea what we're talking about. If this is a result of QM and it holds in the large, no fundamentals have been defined for the conglomerate. That is, the exact atomic states of the protons and the electrons, dismissing mass as a fundamental measure within an atomic state, is never defined. This is only an imaginative response to an elemental function, i.e. the behaviour of a set of charges, a very specific state that is not defined. Hence, what?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.