Browsing by Author "Chan, Kwaichow B."
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Item Localization and local motion of muons in antiferromagnetic oxides: vanadium oxide and iron oxide(Texas Tech University, 1986-05) Chan, Kwaichow B.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.Item Muon sites in transition-metal oxides(Texas Tech University, 1988-08) Chan, Kwaichow B.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.