Molecular nanomagnets are clusters of magnetic metal ions held together with molecular glue. These materials have been successfully studied with a variety of techniques but attempts to use muons as magnetometers have provided puzzling results. In J. Phys.: Condens. Matter 23 242201, a team led by researchers at Oxford University reports how they have unambiguously detected the crossing of the molecules' energy levels using muons.
Molecular nanomagnets are of great interest to researchers as they represent well-defined quantum mechanical systems which may be of future use as elements of quantum computers. These systems often have large values of spin angular momentum and quantum energy levels that can be tuned in an applied magnetic field. At a critical magnetic field, the energy levels cross and the molecule's ground state below the crossing will be different to that above. These level crossings have been studied with a variety of experimental techniques, but attempts to detect them with muons have proven unsuccessful until now.
In J. Phys.: Condens. Matter 23 242201, Tom Lancaster and Stephen Blundell of Oxford University, with collaborators from the ISIS facility and the University of Manchester, show the first example of an energy level crossing in a nanomagnet detected with muons. Muons are subatomic particles which may be implanted into materials. Their interactions provide information on magnetism, superconductivity, charge transport and dynamics. The measurements were made using the newly built HIFI instrument at the ISIS Facility, UK. This spectrometer allows magnetic fields of up to 5T to be applied during a muon experiment, and these are some of the first published results from this instrument.
This work demonstrates that muons are a useful probe of molecular nanomagnets and a promising tool for future research in this area. Because the muons are implanted inside the molecule, they provide a unique perspective for studying the quantum tunnelling that can occur in these new materials.
The Cr8Cd molecule
Tom Lancaster and Stephen Blundell
Research date: July 2011