B. D. Patterson

Local magnetic field at a positive muon in ferromagnetic gadolinium

Abstract The local magnetic field at a stopped positive muon has been measured in polycrystalline gadolinium as a function of temperature between 20 K and the Curie point. The measurements show that the muon occupies the octahedral interstitial site and demonstrate the sensitivity of the muon as a probe of the local magnetic structure.

Internal magnetic fields in the high-temperature superconductor YBa2Cu3O7−δ from muon spin rotation experiments

Muon spin rotation (μSR) measurements of the internal magnetic fields in sintered YBa2Cu3O7−δ samples are reported. Pronounced differences between field-cooled (FC) and zero-field-cooled (ZFC) μSR signals, hysteresis effects and flux trapping are observed. The μSR results are compared with the results of macroscopic experiments (susceptibility, magnetization, resistivity) and with predictions obtained from models of weakly-coupled superconducting regions.

Internal magnetic fields in the high-Tc superconductors La1.8Sr0.2CuO4 and YBa2Cu3O7−δ from muon spin rotation experiments

Abstract Measurements of the internal magnetic field in the high- T c superconductors La 1.8 Sr 0.2 CuO 4 and YBa 2 Cu 3 O 7−δ have been performed after zero-field cooling using the muon spin rotation (μSR) technique. Temperature-dependent changes are observed below T c in both the magnitude of the internal field and the fraction of muons which experience this field.

Absolute sign of the Mu* hyperfine parameters in diamond

Standard μSR experiments in diamond have shown that the relative sign of the hyperfine parameters of the anisotropic Mu* state is negative (A‖/A⊥<0). We report an experimental determination of theabsolute sign of the Mu* hyperfine parameters by studying the transferred muon polarization during the thermally-activated transition from the isotropic Mu state to Mu*. The results demonstrate that the isotropic part of the Mu* hyperfine interaction is negative. In a nitrogen-poor diamond, both the Mu disappearance rate and the enhancement of the Mu* signals are well-described by a single Arrhenius law.

Hydrogen in and on natural and synthetic diamond

Abstract Diamond, both natural and metastable as well as stable growth synthetic, is a material of particularly attractive physical properties. In the characterization of diamond, light volatiles appear to play a significant role both in the determination of properties and in the control of the growth process itself. Historically nitrogen was perceived as the dominant impurity in natural diamond, but in the past decade both oxygen and hydrogen have been shown to be prolific to largely the same degree. This paper takes stock of the state of the art in the study of hydrogen in and on diamond of both natural and synthetic genesis. This includes the study of the surface and bulk hydrogen depth distribution as assayed by traditional nuclear reaction analysis, as well as recent high resolution resonant nuclear reaction analysis of hydrogen as it formally addresses the true surface of diamond. These analytical approaches are valuably complemented by the more subtle use of time dependent perturbed angular distribution studies which are shown to pick out a molecular hydrogen component in the bulk of diamond. Positively charged muons may combine with electrons to form the atom “muonium”, which for all practical purposes disports itself as a light isotope of hydrogen: muonium spin rotation studies are exploited in a radiation damage free manner to study the properties of hydrogen in diamond. Finally some specific work on hydrogen in CVD diamond (-like) materials is considered.

Internal magnetic fields in YBa2Cu3O7−δ from Muon spin rotation experiments: Discussion in terms of a glasslike superconducting state

Muon spin rotation (μSR) measurements of the internal magnetic fields in YBa2Cu3O7−δ are reported. Pronounced differences between field-cooled (FC) and zero-field-cooled (ZFC) μSR signals, hysteresis effects and flux trapping are observed. The μSR depolarization rate provides information regarding the local magnetic field distribution in the superconducting state. The present results show similarities to calculations that model a glasslike superconducting state.

Resolved nuclear hyperfine structure of muonium centres in CuCl and GaAs by means of the avoided-level-crossing technique

Abstract Avoided-level-crossing resonances from isotropic muonium centres interacting with neighbouring nuclear spins in powdered CuCl are reported. The prominent resonances have a complex multiline structure and are strongly temperature-dependent. In addition, previously unobserved resonances in single-crystal GaAs from anomalous muonium interacting with a 71 Ga neighbour are presented.

Muon decay channeling in silicon

The angular distribution of positrons from muon decay in an oriented [111] Si wafer shows a symmetric pattern of six lines of minimum counting rate radiating from a central minimum. The pattern results from positron blocking by the (110) planes and [111) axis. The measurement technique and the dependence of the features on positron energy, muon implanation depth and sample temperature are discussed.

Muon spin rotation studies at SIN

Recently the accelerator and the muon channel at SIN became operational. We report here on some of the first positive muon spin rotation experiments at SIN. The first experiment we discuss concerns the chemistry of muonium. We have observed for the first time a muonium or radical signal in pure water. Next, we discuss the application of the positive muon for the study of ferromagnetic metals and alloys. First measurements on a single crystal of iron around liquid helium temperature seem to indicate that at low temperature the muon does not diffuse. We further report on the first stroboscopic observation of the muon spin rotation which will allow one to take full advantage of the high stopping density at SIN.