Graphite mimics iron's magnetism

October 4, 2009
The electron density of states on a grain boundary of defects. The arrows (pointing in the reader’s direction) indicate the direction of the magnetic moments. Credit: Kees Flipse, Eindhoven University of Technology

Researchers of Eindhoven University of Technology and the Radboud University Nijmegen in The Netherlands show for the first time why ordinary graphite is a permanent magnet at room temperature. The results are promising for new applications in nanotechnology, such as sensors and detectors. In particular graphite could be a promising candidate for a biosensor material. The results will appear online on 4 October in Nature Physics.

Graphite is a well-known lubricant and forms the basis for pencils. It is a layered compound with a weak interlayer interaction between the individual (graphene) sheets. Hence, this makes a good lubricant.

It is unexpected that graphite is ferromagnetic. The researchers Jiri Cervenka and Kees Flipse (Eindhoven University of Technology) and Mikhail Katsnelson (Radboud University Nijmegen) demonstrated direct evidence for ferromagnetic order and explain the underlying mechanism. In graphite well ordered areas of carbon atoms are separated by 2 nanometer wide boundaries of defects. The electrons in the defect regions (the red/yellow area in picture 1) behave differently compared to the ordered areas (blue in picture 1), showing similarities with the electron behaviour of ferromagnetic materials like and cobalt.

This is a two-dimensional plane of magnetically coupled grains of defects. Credit: Kees Flipse, Eindhoven University of Technology

The researchers found that the grain boundary regions in the individual carbon sheets are magnetically coupled, forming 2-dimensional networks (picture 2). This interlayer coupling was found to explain the permanent magnetic behaviour of graphite. The researchers also show experimental evidence for excluding magnetic impurities to be the origin of ferromagnetism, ending ten years of debate.

Surprisingly, a material containing only can be a weak ferro magnet. This opens new routes for spintronics in carbon-based materials. Spins can travel over relative long distances without spin-flip scattering and they can be flipped by small magnetic fields. Both are important for applications in spintronics. Carbon is biocompatible and the explored magnetic behaviour is therefore particularly promising for the development of biosensors.

More information: The paper in "Room-temperature ferromagnetism in graphite driven by 2D networks of point defects" by Jiri Cervenka, Mikhail Katsnelson and Kees Flipse will appear online Sunday 4 October. The paper can be found under DOI 10.1038/NPHYS1399

Source: Eindhoven University of Technology

Explore further: Researchers Find Better Way To Manufacture Fast Computer Chips

Related Stories

Recommended for you

Graphene under pressure

August 25, 2016

Small balloons made from one-atom-thick material graphene can withstand enormous pressures, much higher than those at the bottom of the deepest ocean, scientists at the University of Manchester report.

Designing ultrasound tools with Lego-like proteins

August 25, 2016

Ultrasound imaging is used around the world to help visualize developing babies and diagnose disease. Sound waves bounce off the tissues, revealing their different densities and shapes. The next step in ultrasound technology ...

Nanovesicles in predictable shapes

August 25, 2016

Beads, disks, bowls and rods: scientists at Radboud University have demonstrated the first methodological approach to control the shapes of nanovesicles. This opens doors for the use of nanovesicles in biomedical applications, ...

Neuromorphic computing mimics important brain feature

August 18, 2016

(Phys.org)—When you hear a sound, only some of the neurons in the auditory cortex of your brain are activated. This is because every auditory neuron is tuned to a certain range of sound, so that each neuron is more sensitive ...

'Artificial atom' created in graphene

August 22, 2016

In a tiny quantum prison, electrons behave quite differently as compared to their counterparts in free space. They can only occupy discrete energy levels, much like the electrons in an atom - for this reason, such electron ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

PPihkala
not rated yet Oct 06, 2009
Yeah, pencil seems to be be attracted to permanent magnet. Only slightly, but still detectably.

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.