Probing interaction of paramagnetic electron with conduction electrons in high Tc superconductor LaSrCuO by (μ-O) spin relaxation

The paramagnetic (μ^-O) state formed at the oxygen site in high T_c LaSrCuO was used to probe an interaction between the localized moment of the paramagnetic electron and the conduction electrons via zero field μ^- spin relaxation. The enhanced relaxation rates consistently observed in the superconducting state of various Sr concentrations are explained as an effect of spin‐pairing in the high T_c supercurrent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Studies of diluted antiferromagnets MnxMg1-xTiO3 with x=0.55 and 0.70 by muon spin relaxation method

Longitudinal fields μSR measurements have been performed in order to probe the spin dynamics in the diluted antiferromagnets Mn_xMg_1-xTiO₃ with x=0.70 and 0.55. In the x=0.70 sample which forms the antiferromagnetic long‐range order, the static and fluctuating fields coexist at the muon stopping site below T_N. On the other hand, in the x=0.55 sample which shows the spin‐glass behavior, the local fields fluctuate rather fast even below T_SG. We infer that this drastic change occurs when Mn_xMg_1-xTiO₃ transforms from an antiferromagnetic system to a spin‐glass system by dilution. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mu centers in crystalline Ge under illumination

A slow conversion to a diamagnetic state has been observed for muonium centers at the tetrahedral interstitial site (Mu⁰ _T) in dark Ge at low temperatures. While the conversion process is affected by illumination, no effect of illumination upon the initial (Mu⁰ _T) centers themselves was observed at 10 K. This is in marked contrast with the case of (Mu⁰ _T) centers in Si where strong interaction with photo‐induced carriers is observed, suggesting that the electronic level associated with (Mu⁰ _T) state in Ge is not located in the energy gap. This revised version was published online in August 2006 with corrections to the Cover Date.     

µCF experiments in thin deuterium films and progress towards slow µ− production

Muon-catalyzed fusion was investigated in thin solid deuterium films to determine the experimental feasibility of slow µ^– production by detection of dd fusion protons as well as slow µ^– collection utilizing a large-acceptance magnetic spectrometer. The spatial distribution of the fusion reaction in the film was extracted, and an optimum thickness for slow µ^– emission was deduced. Collected 10 keV µ^– were also successfully detected. However, the dd fusion yield being insufficient, we were not able to distinguish slow µ^– via µCF from degraded µ^–.     

Diffusion of positive muons in zone-refined iron below room temperature

The relaxation rate λ of μ⁺ spin in α-iron polycrystals and single crystal of 99.995% purity has been measured from 299 down to 50 K. At room temperature it is 0.14 μsec^-1, much smaller than ever observed. Above 120 K its temperature dependence obeys an Arrhenius law (activation energy 44 ± 3 meV) for the μ⁺ diffusion. Previous values in less pure samples are discussed in terms of internal field inhomogeneity and of μ⁺ trapping by chemical or non-chemical defects. The deduced diffusion rate is proportional to T² in the whole temperature region studied.     

Muonium reaction with nitrogen dioxide

The reaction rate of the reaction of Mu and NO₂ was measured by means of transverse field MuSR in Ar gas containing NO₂. A pulsed surface muon beam was employed for the experiment. The rate constant of the reaction was found to be substantially larger than that of the analogous H reaction.