Graphite mimics iron's magnetism

Oct 04, 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: Nanotube cathode beats large, pricey laser

add to favorites email to friend print save as pdf

Related Stories

A slice of carbon could work wonders with chips

Apr 21, 2006

Move over silicon: the hottest new material in electronics could be sitting inside the humble pencil. At the Institute of Physics' Condensed Matter and Materials Physics conference at the University of Exeter on Thursday ...

By adding graphene, researchers create superior polymer

May 19, 2008

Researchers at Northwestern University and Princeton University have created a new kind of polymer that, because of its extraordinary thermal and mechanical properties, could be used in everything from airplanes to solar ...

Nano World: Composites with nano-graphite

Jul 24, 2006

Strong, lightweight plastic-like composites made with highly electrically conductive sheets of carbon just one atom thick could find use in electronics and protect aircraft from lightning strikes, experts told UPI's Nano ...

Recommended for you

Ultrafast remote switching of light emission

4 hours ago

Researchers from Eindhoven University of Technology can now for the first time remotely control a miniature light source at timescales of 200 trillionth of a second. They published the results on Sept. 2014 ...

Nanotube cathode beats large, pricey laser

11 hours ago

Scientists are a step closer to building an intense electron beam source without a laser. Using the High-Brightness Electron Source Lab at DOE's Fermi National Accelerator Laboratory, a team led by scientist ...

User comments : 1

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.