Negative muon spin rotation at oxygen site in paramagnetic MnO

The negative-muon spin-rotation method (μSR) has been applied in order to observe the hyperfine field at μ-O in paramagnetic MnO at room temperature. The oxygen atom in this magnetic oxide plays an important role in the superexchange interaction which gives rise to antiferromagnetic ordering of Mn2+ d-electrons below Tsub(N) = 116 K. The present result indicates that (i) the presence of μ- at O increases the local covalency and thus enhances the local superexchange interaction, which gives rise to a reduction of the polarization of the neighbouring Mn2+ d spins, and that (ii) the local exchange frequency is also increased, so as to reduce the relaxation rate. (Auth.)