Electronics is undergoing somewhat of a revolution with the advent of three new disciplines in recent years: spintronics, molecular electronics and quantum computing. All three of these disciplines rely on molecular magnets, which combine the classic macroscale properties of a magnet with the quantum properties of a nanoscale structure. Being able to characterize molecular devices, such as molecular spin transistors and spin valves, made from these tiny magnets is thus becoming more and more important.

A team led by Wolfgang Wernsdorfer at the Institut Néel in Grenoble, France, has built a carbon nanotube resonator to this end. The researchers began by patterning platinum electrodes next to each other separated by a deep trench over which they then grew carbon nanotubes using chemical vapour deposition. This particular process ensures that the resonator produced has the best mechanical properties, explains Wernsdorfer.

Nanotube oscillations

Next, the team, which includes scientists from the Karlsruhe Institute of Technology in Germany and the University of Strasbourg, France, functionalized the carbon nanotube oscillator with molecules carrying a well defined magnetic moment. When the moment of a molecule reverses, this causes the nanotube to oscillate, which in turn produces a change in the current passing through the nanotube. This change can be used to determine the nuclear spin of the molecule in question.

“The strong coupling between the nanotube and the magnetic molecule means that such a resonator can be used as an ultrasensitive magnetometer,” Wernsdorfer told nanotechweb.org. “Going beyond simple magnetometry, such coupling could also be exploited to manipulate a magnetic molecule using the resonator and vice versa – something that might reveal various quantum mechanical effects, such as quantum coherence.”

The researchers, who are working in close collaboration with the European Institute of Molecular Magnetism, have been busy working in this field for several years now. For example, they have already built a novel spin-valve device in which a non-magnetic molecular quantum dot – consisting of a single-walled carbon nanotube contacted with non-magnetic electrodes – is laterally coupled via supramolecular interactions to a TbPc2 molecular magnet. The localized magnetic moment of the single-molecule magnet (SMM) leads to a magnetic-field dependent modulation of the conductance in the nanotube with magnetoresistance ratios of up to 300% below temperatures of 1K, says Wernsdorfer.

“We have also succeeded in reading out the nuclear spin of an individual metal atom embedded in a SMM using a molecular spin transistor,” he added. “And, we have provided the first experimental evidence for strong spin-phonon coupling between the single molecule’s spin and a carbon resonator. Our work could help develop new spintronics devices with quantum properties, which is the main goal of our project.”

The group’s research is detailed in Nature Nanotechnology.