P. F. Meier

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.

Cluster calculations of muonium states in semiconductors

The electronic structure of interstitial hydrogen in diamond, silicon and germanium is investigated by means of cluster calculations on the level of the unrestricted Hartree-Fock self-consistent field approximation. A stable configuration for H is found at a bond-centred site and its hyperfine properties are compared to experiments on paramagnetic muonium states.

Exact calculation of the muon polarization function

The spin dynamics of a polarized muon at an interstitial lattice site interacting with four or six nearest neighbouring nuclear spins withJ=1/2 has been investigated. The difference from the results of the Kubo-Toyabe theory is pointed out. The interaction of a muon with four nuclei with spinJ=1 including both dipolar and quadrupolar effects is considered, and some numerical results are shown.

An efficient algorithm to determine fractal dimensions of point sets

Abstract Based on the Grassberger–Procaccia approach, an efficient, box assisted algorithm for the determination of the correlation dimension D 2 of a finite point set is presented. By invoking a tree like data structure, we are able to handle arbitrary box dimensions d B and consequently enhance the efficiency of the calculation compared to methods which only allow for low d B . The CPU-time consumption of our algorithm is compared to that of the standard implementation by applying both methods to the system of three uncoupled Henon maps. A considerable efficiency gain is shown.

First-principles calculations of hyperfine interactions inLa2CuO4

We present the results of first-principles cluster calculations of the electronic structure of

Passivation of boron in silicon by hydrogen and muonium: calculation of electric field gradients, quadrupole resonance frequencies and cross relaxation functions

{\mathrm{La}}_{2}{\mathrm{CuO}}_{4}.

μSR in antiferromagnetic α-Fe2O3☆

Several clusters containing up to nine copper atoms embedded in a background potential were investigated. Spin-polarized calculations were performed both at the Hartree-Fock level and with density-functional methods with generalized-gradient corrections to the local-density approximation. The distinct results for the electronic structure obtained with these two methods are discussed. The dependence of the electric-field gradients at the Cu and the O sites on the cluster size is studied and the results are compared to experiments. The magnetic hyperfine coupling parameters are carefully examined. Special attention is given to a quantitative determination of on-site and transferred hyperfine fields. We provide a detailed analysis that compares the hyperfine fields obtained for various cluster sizes with results from additional calculations of spin states with different multiplicities. From this we conclude that hyperfine couplings are mainly transferred from nearest-neighbor

μSR in ferromagnetic and antiferromagnetic dysprosium

{\mathrm{Cu}}^{2+}

Theoretical study of the Cox-Symons model for normal muonium in silicon

ions and that contributions from further distant neighbors are marginal. The mechanisms giving rise to transfer of spin density are worked out. Assuming conventional values for the spin-orbit coupling, the total calculated hyperfine interaction parameters are compared with those derived from experiments.

Temperature dependence of hyperfine fields at impurities in metals

The possibility of studying impurity passivation complexes in semiconductors by quadrupole resonance spectroscopy is examined. The problem is illustrated for the case of boron in silicon passivated with hydrogen or, equivalently, with muonium, since the radioactive light isotope in principle offers a greater sensitivity for detection of the spectra. Ab initio calculations on suitable cluster models of the passivation complexes provide estimates of the electric field gradients at the quadrupolar nuclei, and thereby predictions of the quadrupole resonance frequencies. Detection via cross-relaxation techniques is proposed, notably muon level crossing resonance ( mu LCR), and illustrated by calculation of the time dependence of the muon polarization function. Possible reasons for the absence of quadrupolar resonances in mu LCR spectra recorded in exploratory experiments are discussed: these include the existence of a local tunnelling mode for the lighter isotope.