The trigonal bipyramid: a new building block for making frustrated magnets
From compasses to iPods, magnets are the basis of many technological applications.
Our understanding of magnetism is based around the idea of atomic-level spins and the interactions between them. Positive interactions result in a ferromagnet with all spins aligned, whereas negative interactions (antiferromagnetic, AF) between spins give rise to more complicated magnets. AF spins located on a two dimensional (2-D) square produce an arrangement with alternating spins. However, it’s not possible for AF spins on the vertices of triangles to align themselves so that all of their interactions with their neighbours are satisfied. In this case the system is said to be ‘frustrated’. An example of a frustrated 2-D magnet, named after a Japanese weaving technique, is the kagome lattice. In real systems, 2-D kagome layers (KL) are coupled together through other layers that tend to break the frustration. It is generally thought that the best way to keep the KL frustrated is to decouple them to reduce these interlayer interactions.
Using a combination of neutron scattering and computer simulations on a kagome like system YBaCo4O7, we show that in fact, strong coupling between the KL can help to keep them frustrated. Our model also introduces a new magnetic entity, a trigonal bipyramid, where the sum of the basal spins is opposite to the sum of the apex spins.
P Manuel, LC Chapon (ISIS), PG Radaelli (Oxford University), JF Mitchell, H Zheng (Argonne National Laboratory, USA)
Contact: Dr P Manuel, Pascal.Manuel@stfc.ac.uk; LC Chapon, Laurent.Chapon@stfc.ac.uk
Further reading: P Manuel, LC Chapon et al., Phys Rev Lett 103 (2009) 037202