Carel Boekema

Magnetic Dynamics in Oxides, As Observed by Muon Spin Relaxation

Recent and earlier magnetic-oxide investigations by means of the muon-spin-relaxation (µSR) technique are reviewed. The dynamics of the processes in the observed phase transitions, as probed by the muon, as well as of the behavior (probing, bonding and motion) of the muon “spy” will be discussed. The main emphasis will be on the µSR studies on a-Fe2O3 (hematite), Fe3O4 (magnetite) and V2O3 (karelionite). Electron-phonon interactions appear to be major ingredients in the physical origins of the magnetic and metal-to-insulator phase transitions seen in karelionite and magnetite.

Magnetic frustration, muon probing, and hydrogen bonding in RBa2Cu3Oy

Abstract Recent muon-spin-relaxation (μSR) studies on (Pr x Y 1−x )Ba 2 Cu 3 O y and H z YBa 2 Cu 3 O 7 have confirmed the muon-probe site location near the BaO planes. Similar behavior for H + in Hydrogen-doped YBa 2 Cu 3 O 7 is seen as has been observed for the μ + , namely bonding with oxygen. Thus, the knowledge of the muon-probe site in R123y improves the interpretations of the μSR magnetic studies in (Pr x Y 1−x ) 1237 and the μSR vortex studies in R1237. Magnetic frustration appears to be the key to resolve the physical origin of the CuO-based superconductivity.

Mössbauer spectroscopy and magnetic properties of copper-304 stainless steel multilayer films

The magnetic behavior of multilayer films of Cu-304 stainless steel (304SS) with equal layer thickness fabricated by magnetron sputtering at ambient temperature is reported. For small layer thickness (t=0.5–1.0 nm), the films show epitaxial fcc growth of 304SS on fcc copper, and multilayers are nonmagnetic due to nonmagnetic nature of fcc 304SS. For larger layer thickness (t=1.0–50.0 nm), 304SS grows epitaxially as fcc near the copper interface accompanied by a bcc 304SS growth away from the interface. As a result, two regimes are observed in 1.0–50.0 nm thickness range. Medium layer thickness (t=1.0–1.35 nm) multilayers show weak ferromagnetism characterized by small magnetization due to comparable thickness of ferromagnetic bcc 304SS and nonmagnetic fcc 304SS. A strong ferromagnetic behavior is observed for thick samples (t=1.35–50.0 nm) due to 304SS layer being primarily ferromagnetic bcc phase with very small percentage of fcc near the interface. Mossbauer effect spectroscopy and magnetometry were uti...

Muon and hydrogen bonding, and magnetic resonance in pure and doped 519-01519-01519-01

Results of three magnetic resonance studies on pure and doped YBa2Cu3O7 (Y1237) are compared. The muon and the proton, in low concentrations, behave similarly in these cuprates; both magnetic probes bond to oxygens just below the BaO planes. Phase changes from superconducting to magnetic behavior of H-doped Y1237 correspond to similar transitions observed for either 0 depletion or (Pr,Y) mixing. Chemical phase-separation effects are unlikely to be responsible for the simultaneous observation of superconductivity and magnetism. The similarity of the physical effects caused by H doping, O depletion, or (Pr, Y) mixing in the 1/2/3 cuprates points toward a plausible magnetic origin of CuO-based superconductivity.

Wannier states in magnetite

Magnetite exhibits the well‐known metal–insulator transition at the Verwey temperature (TV) near 123 K. Neither the physical origin nor the conduction process above TV is well understood. Using the Cullen and Callen tight‐binding Hamiltonian, the ‘‘extra’’ fully spin‐polarized 3d conduction electrons in the B sublattice are described. By introducing a covalency parameter Γ, the Wannier states for these conduction electrons can be characterized. Only for the lower singlet subband, does the Γ value point toward delocalization. The results reveal that the Wannier states in magnetite are a mixture of localized and delocalized electron states.

Muon Spin Relaxation: A Novel Magnetic Resonance Technique to Study Dynamic and Static Magnetism

The novel muon-spin-relaxation technique is discussed in some detail with emphasis on the application in Solid State Physics, and especially with regard to studies in dynamic and static magnetism. A comparison with other magnetic resonance techniques is given. A future outlook on muon spin research in magnetic dynamics is presented.

Muon Spin Research on Spin Glasses

Major results of muon-spin-relaxation (µSR) studies on canonical and oxide spin glasses are discussed. The metallic spin glasses AgMn, AuFe, CuMn, and CuFe and the oxide spin glass Fe2Ti05 are highlighted. The µSR work shows clearly that below the spin-glass temperature (Tg) both slow and rapid spin fluctuations occur. Single-crystal µSR investigations indicate that the freezing process in spin glasses is spatially inhomogeneous, whereas polyerystalline-sample µSR results point toward a dominantly homogeneous freezing process. Currently, the model descriptions of the dynamics in spin glasses observed above Tg are not unanimous; anisotropy appears to be the necessary ingredient to attempt to solve this problem in spin dynamics.