An outsider’s view: a novel muon study of frustration

an oscillatory signal

An oscillatory signal in the muon data is a clear indication of static internal magnetic fields in Tb2Sn2O7. The inset shows the temperature depence of the internal field below the transition.
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Frustration occurs when it is not possible to satisfy all interactions between atoms.

As described in 'The trigonal pyramid: a new building block for making frustrated magnets', a magnetic atom might want its spin direction to be misaligned with that of a neighbouring atom (if the interactions are antiferromagnetic).  But for some arrangements of atoms, misalignment with one neighbour prevents misalignment with another – producing frustration.  Frustration plays an important role in a diverse range of physics, from magnetism to protein folding. Pyrochlores – magnetic materials with atoms arranged in a way that leads to frustration –  are fascinating as by changing one atom the frustration behaviour changes, culminating in properties such as a ‘spin liquid’, ‘spin glass’ or ‘spin ice’.

The frustration in pyrochlore Tb2Sn2O7 has previously led some to believe it exhibits a novel state of magnetism in which the magnetisation direction reverses multiple times a second. This is not how a permanent magnet normally behaves. We tested the behaviour using muons implanted into silver in front of the sample (rather than into the sample itself). If the sample behaved like a permanent magnet, its field lines would penetrate the silver and be detectable by the muons. This is indeed what is revealed – so that Tb2Sn2O7 does in fact  behave like a permanent magnet below its transition temperature of 0.87K.

 

SR Giblin, JDM Champion (ISIS), HD Zhou and CR Wiebe (Florida State University, USA), JS Gardner (NIST, USA), I Terry (Durham University), S Calder, T Fennell, ST Bramwell (University College London)

Contact: Dr Sean Giblin, sean.giblin@stfc.ac.uk

Further reading: SR Giblin et al., Phys Rev Let 101 (2008) 237201

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