Sensitivity and fatigue of LiTaO3 for holographic recording

The sensitivity of crystals of LiTaO3 to hologram formation was observed to vary with impurity concentration from a value comparable to the most sensitive doped LiNbO3 for an impure crystal to a value more than five orders of magnitude smaller for a purer crystal. Fatigue effects were observed upon write-erase cycling. These effects were dependent upon writing and erasure polarization and power and could be virtually eliminated by proper choice of optical parameters

An EPR investigation of the dynamic Jahn-Teller effect in SrCl2-La/2 plus/

Second-order solutions of Hamiltonian functions for EPR study of Jahn-Teller effect in SrCl2-La/2 plus

Magnetic interaction of Co ions near the {10\bar{1}0} ZnO surface

Co-doped ZnO is the prototypical dilute magnetic oxide showing many of the characteristics of ferromagnetism. The microscopic origin of the long range order however remains elusive, since the conventional mechanisms for the magnetic interaction, such as super-exchange and double exchange, fail either at the fundamental or at a quantitative level. Intriguingly, there is a growing evidence that defects both in point-like or extended form play a fundamental role in driving the magnetic order. Here we explore one of such possibilities by performing {\it ab initio} density functional theory calculations for the magnetic interaction of Co ions at or near a ZnO \{10$\bar{1}$0\} surface. We find that extended surface states can hybridize with the $e$-levels of Co and efficiently mediate the magnetic order, although such a mechanism is effective only for ions placed in the first few atomic planes near the surface. We also find that the magnetic anisotropy changes at the surface from an hard-axis easy-plane to an easy axis, with an associated increase of its magnitude. We then conclude that clusters with high densities of surfacial Co ions may display blocking temperatures much higher than in the bulk

Molecular Dynamics of the Muonium-C60 Radical in Solid C60

The molecular dynamics and electronic structure of the μ+-C60 radical in crystalline C60 have been studied using muon spin rotation and relaxation. At room temperature μ+-C60 appears to be in a state of quasifree rotation. At the critical temperature TS=260 K the local electronic structure and molecular dynamics change discontinuously as expected for a first-order phase transition. The correlation times for reorientation are remarkably close to those determined by recent NMR experiments on C60, suggesting that the molecular dynamics of μ+-C60 are strongly coupled to those of its C60 neighbors

Depolarization of diffusing spins by paramagnetic impurities

The depolarization of diffusing spins (muons) interacting with dilute paramagnetic impurities in a solid was studied using a simple computational model which properly treats the muon motion and preserves correct muon-impurity distances. Long-range (dipolar) and nearest-neighbor (contact) interactions are treated together. Diffusion parameters are deduced and model comparisons made for AuGd (300 ppM)