Localization and local motion of muons in antiferromagnetic oxides: vanadium oxide and iron oxide

The behavior of muons in the antiferromagnetic insulating oxides, a-Fe203 sirid V2O3 has been examined using dipole field calculations. The results verify muon sites suggested by potential calculations for hydrogen in similar systems, and imply the formation of muon-oxygen bonds at low temperatures. In both of these corundum structured oxides two sets of muon sites are located, each approximately lA from an oxygen ion. These are the Rodriguez sites in the vacant octahedral interstices of the oxygen ions and the Bates sites near the oxygen basal plane. Only a subset of sites found in a-Fe203are also found V2O3 because of a slight distortion of V2O3 from rhombohedral to monoclinic symmetry below the metal-insulator temperature at 155K.

Above 350K, muons diffuse globally and no MuSR precession signal is observed. At intermediate temperatures, between 120K and 350K, muons diffuse locally as illustrated in the case of a-Fe203. Calculations show that diffusion among a subset of sites is consistent with the data in this temperature range. It is concluded that muon-oxygen bonding and motion among a group of closely spaced sites are the low temperature localized states for muons in the corundum structured oxides.