Magnetic insights: Playing the percentages

Skip to Navigation

Ezine

  • Published: Jul 15, 2013
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Magnetic insights: Playing the percentages

Wiring up

So sensitive. When a magnetic field is switched on, electrons are unable to migrate from a conductive surface (blue) through chains of molecules encapsulated in a crystal to the tip of an atomic force microscope (grey). Credit: W. G. van der Wiel/University of Twente

An international research team has shown that one-dimensional molecular conducting wires can be switched to an insulating state using a weak magnetic field even at room temperature. The finding might offer new insights into the innate navigation systems of migratory birds as well as leading to new technology for magnetic field sensors, inexpensive touch screen displays and high-density magnetic storage for smart phones and other portable devices.

Scientists at MESA+, the research institute for nanotechnology at the University of Twente have collaborated with teams at the University of Strasbourg, in France, Karlsruher Institut für Technologie, Germany and Eindhoven University of Technology to create near-perfect one-dimensional molecular wires that respond to a magnetic field. The electrical conductivity of the drops almost completely when the wire experiences even a weak magnetic field - just a few milliteslas, the strength of an everyday "fridge magnet" - at room temperature. This represents a 2000% magnetoresistance change. By comparison, the giant magnetoresistive materials discovered in the 1980s and used in computer hard drives approached an effect of 110% and tunnelling magnetoresistance materials pushed this up to 600% in 2002.

Speeding up

Writing in the journal Science, the team explains how they prepared wires using the red dye molecule DXP, which is non-magnetic and perhaps most famous as the red of Ferrari's Testarossa sports car. The team locked the DXP into one-dimensional chains of 30 to 100 nanometres length using the porous structure of a zeolite L crystal, an insulating aluminosilicate. The zeolite pores are a mere 1 nanometre in diameter, just enough to allow the DXP to fit in the hollows. A thin film of the composite was then applied to an electrically conducting substrate.

The team then used the conductive needle of an atomic force microscope (AFM) touching the upper surface of the zeolite to measure the electrical conductivity in the molecular chains. According to team leader Wilfred van der Wiel being able to measure the conductivity of wires trapped in this way in itself is a unique experiment. However, it is with the application of a weak magnetic field that the most interesting aspect of the work is manifest. Van der Wiel says that the strength of the observed phenomenon is "very special."

A flight of fancy

The researchers suggest a possible mechanism for the drop in conductivity in the Pauli Exclusion Principle. As the molecular wires are essentially one-dimensional, Pauli has a dramatic effect leading to a blockage on these single-lane routes and preventing electron flow. The mechanism is supported by their calculations. "We are trying to 'get rid of' the conducting probe AFM now, so that we can measure the effect in real devices," van der Wiel told SpectroscopyNOW. "This should help to study the effect in much more detail. Ultimately, we hope to understand the physics to its full extent and to develop a system that is also technologically applicable."

It will then be down to technologists to find ways to exploit this effect in devices. Meanwhile, the team is now conducting follow-up experiments to see whether or not the phenomenon might have any bearing on avian navigation in migratory birds.

Related Links

Science 2013, online: "Ultra-High Magnetoresistance at Room Temperature in Molecular Wires"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Social Links

Share This Links

Bookmark and Share

Microsites

Suppliers Selection
Societies Selection

Banner Ad

Click here to see
all job opportunities

Copyright Information

Interested in separation science? Visit our sister site separationsNOW.com

Copyright © 2017 John Wiley & Sons, Inc. All Rights Reserved