Muon spin rotation

All in a spin: an unstable radioactive particle can glean secrets from novel magnets and superconductors.

A muon is an unstable spin-1/2 particle with a lifetime of 2.2 μs. Beams of spin-polarized positive muons can be prepared at accelerator facilities and then subsequently implanted in various types of condensed matter. Both the time and direction dependence of the subsequent positron emission can be monitored. This allows the precession and relaxation of the average muon-spin polarization to be measured and the local magnetic field in the sample to be directly inferred. The muon thus behaves essentially as a ‘microscopic magnetometer’ and is used to follow the magnetic order at a local level and to investigate both static and dynamic effects.

Muon-spin precession signal in the iron-based superconducting system NaFeAs. These precession oscillations tell us about the magnetic order in this material. The superconducting state strengthens as you selectively replace a small percentage of Fe atoms with Co. See Parker et al. Phys. Rev. Lett. 104, 057007 (2010).

Groups using this technique