Anomalous anisotropies and field dependencies of the muon Knight shift and the relaxation rate in monocrystalline Bi

The angular dependence of the muon Knight shift,K _μ, and the muon relaxation rate in Bi at 11 K were measured in external magnetic fields up to 1 T. BothK _μ and the second moment,M ₂, are field dependent and involveP ₄ ⁰(cos θ) andP ₄ ³(cos θ) terms in the angular dependence. The Knight shift behaviour is discussed in terms of the dipole-dipole interaction and the de Haas-van Alphen effect, a consistent interpretation was not achieved in either case. The field dependence ofM ₂ is in complete contrast to the second moment calculations and points to a field dependent redistribution of the charge distribution around the interstitial site.     

Evidence for complex magnetic order in U2Zn17: A μ+ SR studySR study

μ⁺ SR-measurements in transversally applied magnetic fields of 2000 G and 4000 G on heavy-electron single crystal U₂Zn₁₇ are presented. They reveal that at least two types of interstitial sites are occupied by the positive muons. One of these sites (1/3, 2/3, 5/6) could be identified via induced local dipolar fields which aboveT _N=9.7 K can exactly be derived from the magnetic susceptibility. The corresponding component of the μ⁺-signal exhibits a steplike decrease by about 40% atT _N which is caused by the onset of a very broad distribution of static internal magnetic fields (ΔB≈1000 G) with zero average. Such a field distribution is in distinct contrast to dipolar-field calculations performed for the simple antiferromagnetic structure deduced from neutron diffraction. The remaining 60% of the muons contributing to this component belowT _N are subject to a narrow static field distribution (ΔB≈1 G). The induced dipolar fields at the site (1/3, 2/3, 5/6) are temperature-independent belowT _N. A weak dipolar coupling to the U-moments renders similar observations for muons occupying the second type of interstitial impossible.     

Positive muons in bismuth: determination of their sites,detection of a large local lattice contraction and giant associated electric field gradients,evidence for short and long range diffusion

Using a high purity Bi single crystal the temperature and orientation dependence of the zero and transverse field muon spin relaxation rate has been studied in detail. The results imply that the ⁺ occupies one of the two possible interstitial sites in the distorted rhombohedral crystal structure of Bi below 10 K and the other site above 80 K. At both sites the nearest neighbor Bi atoms are found to be shifted towards the ⁺ by 10% of their nominal distance, implying a large local lattice contraction. In concomitance extremely strong electric field gradients are manifest at the nn Bi nuclei. An almost temperature independent reduced relaxation rate in the temperature range from 20 K to 60 K is interpreted in terms of short range diffusion along a limited chain of alternating types of sites. Above 100 K both long range and short range diffusion are indicated.     

Anisotropic muon Knight shift in the HCP single crystals of Cd,Zn and Be

In single crystal samples of Zn, Cd and Be (hcp structure) stroboscopicSR measurements successfully revealed anisotropies in the muon Knight shift (K). An anisotropic K can provide information on the amount of non s-electrons screening the charge of the muon implanted in these metals as a light hydrogen isotope. In Cd, the anisotropic part depends strongly on the temperature and shows a change in sign at roughly 110 K. In Zn, the anisotropic part below 10 K turns out to comprise 4th order contributions in the direction cosines of the external field. This can be understood on the basis of an anisotropicg-factor of the conduction electrons or spin-orbit coupling, respectively.     

Evidence for a two component magnetic response in UPt3

The magnetic response of the heavy fermion superconductor UPt3 has been investigated on a microscopic scale by muon Knight shift studies. Two distinct and isotropic Knight shifts have been found for the field in the basal plane. While the volume fractions associated with the two Knight shifts are approximately equal at low and high temperatures, they show a dramatic and opposite temperature dependence around T(N). Our results are independent on the precise muon localization site. We conclude that UPt3 is characterized by a two component magnetic response.     

Longitudinal field quenching studies in KCl and KBr — Evidence for a precursor muonium state

The repolarization of μ⁺ in a longitudinal field as a function of field strength has been measured at various temperatures in KCl and KBr single crystals. The data at room temperature in KCl are essentially in agreement with Ivanteret al. /1/ and Nishiyamaet al. /5/. The obtained quenching curves can be reasonably fitted by assuming that the long lived muonium state, seen directly in transverse field experiments by Kieflet al. /4/, is preceded by another short lived muonium state with reduced hf-coupling. It is also necessary to allow for electron spin exchange in the precursor state. The model fits yield the hyperfine frequency of the precursor state, its chemical lifetime and an electron spin flip rate. It is speculated that the precursor state and the temperature dependence of the fitted parameters reflect the early history of the μ⁺ in its terminal spur.