Zero-field muon-spin-resonance and lower-critical-field data are presented for a wide range of Th concentrations in Uix Th v Bei3, spanning the region where both a superconducting and a second, lowertemperature phase transition are observed. Overall T-x phase boundaries are assigned and discussed according to the nature of the lower phase transition. Arguments for associating the lower phase with a possible magnetic (time-reversal-violating) superconducting state are given.

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Muon spin depolarization has been studied in moderately concentrated AgMn and AuFe alloys from the freezing temperature T~up to 300 K. The muon depolarization function can be analyzed to show that the temperature dependence of the strongly nonexponential form of the local spin autocorrelation function in these canonical alloys is similar to that observed in numerical simulations on Ising spin glasses. The dynamic behavior above Tg appears to be an intrinsic precursor to spin glass freezing.

%e report muon spin rotation measurements on the antiferromagnetic heavy-fermion superconductor UPd2A13 in the superconductin state. The Lpndon penetration depth is found to be approximately isotropic, A~(0) = 4800~500 and A~~(0) = 4500~500 A. The~+ Knight shift behavior below T, indicates that local moment magnetism and superconductivity are carried by different electron substrates of 5f character, one of which involves the heavy qnasiparticles. For the latter a nearly isotropic magnetic susceptibility g = 1.7 & 10 emu/mole can be estimated. PACS numbers: 74.70.Tx, 75.30.Mb, 76.75.+i The large variations in the ground state properties

This paper is a review of recent progress in the study of +-' interactions of polarized positive muons and muonium (~ e) atoms in matter. These studies are made possible by the asymmetric decay of the muon, in which the easily detected positron is emitted preferentially along the muon spin. A wide range of phenomena are discussed, ranging + from chemical reactions of muonium to uses of the ~ magnetic moment as a microscopic probe of local magnetic fields in solids. Finally, the acronym "~SR" is suggested to describe such studies, in the context of their relationship with various NMR and ESR techniques. '\, 1 asymmetry A would be 3"~' As the detection efficiency + ' \ ,. '-41(". '..i upon beam polarization, counter geometry, and the details of the decay. Both are usually fitted as empirical parameters. Figure 6.1 shows the de

The zero-field muon spin relaxation technique has been used in the direct observation of spontaneous magnetic order below a Curie temperature (T(c)) of approximately 16.1 kelvin in the fullerene charge-transfer salt (tetrakisdimethylaminoethylene)C(60) [(TDAE)C(60)]. Coherent ordering of the electronic magnetic moments leads to a local field of 68(1) gauss at the muon site at 3.2 kelvin (parentheses indicate the error in the last digit). Substantial spatially inhomogeneous effects are manifested in the distribution of the local fields, whose width amounts to 48(2) gauss at the same temperature. The temperature evolution of the internal magnetic field below the freezing temperature mirrors that of the saturation magnetization, closely following the behavior expected for collective spin wave (magnon) excitations. The transition to a ferromagnetic state with a T(c) higher than that of any other organic material is now authenticated.

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Results on the systematics of the magnetic penetration depth k,b in the high-temperature superconductors Bi2Sr~Cal, Y,Cu208+g (z =0,0.1,0.2,0.3,0.4, 0.45) and Bi2 Pb Sr2CaCu208+g(x=0.15,0.30,0.70) are reported from muon-spin-rotation measurements on polycrystalline samples with known oxygen excess 5. In determining A, ,z various additional sources for inhomogeneous internal field distributions, besides the one arising from the Aux-line lattice, have been critically taken into account. The most important one arises from a type of powder broadening due to the anisotropy of the field-cooled magnetization.