When a negative muon (μ-) is implanted into MgH2, the μ- is trapped by the muon atomic orbitals near a Mg nucleus. Since μ- has a polarized spin, we can obtain information about the magnetic field at the Mg nucleus sites, formed by the hydrogen nucleuses, through the observation of how the μ- spin depolarizes with time.  @ J. Sugiyama/Toyota Central Research & Development Laboratories Inc.
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