Muon sites in transition-metal oxides

Muon behavior in a selected series of transition-metal oxides has been investigated by the Muon Spin Rotation (fiSR) technique. The materials studied are the corundum structured oxides (M2O3: M=Fe, Cr, V, Ti) and the high-Tc superconducting oxides in Y-Ba-Cu-0 system. The muon is first implanted into the oxide crystalline and its subsequent behavior in the presence of magnetic field is monitored through counting the positron emitted by the decayed muon. The muon is found to behave like a free muon and to become localized at low temperatures and diffusional at higher temperatures. The location of the muon is important for interpreting the |J.SR data. To identify muon sites, a combination of electrostatic potential and magnetic dipolar field calculation is used. Dipolefield calculation allows matching the experimental results to the calculated values if the origin of the magnetic field is dominantly dipolar as in the case V2O3 and Cr203. In the potential model, in addition to the coulombic interaction, the muon is assumed to form a muon-oxygen bond in analogy to the hydroxyl bond (0H)~. Morse potential is used to simulate the µ+o= bonding. The potential minima found are then assigned as muon sites. A set of muon sites thus found in these oxides and their implications are presented. The inadequacies of the classical model and a more realistic model for predicting muon sites are also discussed.