μ+ relaxation correlated with susceptibility in the van‐Vleck paramagnet PrIn3

A previously unobserved increase of the magnetic susceptibility in PrIn₃ at low temperatures is reported. The increase is shown to correlate nicely with a large increase in the transverse μSR depolarization rate. Evidence supports the conclusion that both phenomena are related to some degree of atomic disorder in the structure, and an associated strong Pr CEF level changes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetic ordering in the T* phase La1.2Tb0.8CuO4

We report a muon spin relaxation study of the magnetic properties of the La_1.2Tb_0.8CuO₄ phase with the T^* structure. Random magnetic order is revealed between 280 and 170 K by the zero field data. A spontaneous muon precession then appears below 170 K, arising from antiferromagnetic long range order of the Cu²⁺ spins. Evidence exists below 20 K for ordering of the Tb³⁺ ions. We find that the T^* phase adopts the same magnetic structure as the (T/O) phase La₂CuO₄.     

μ+SR knight shift in single crystal PrNi5—Evidence for muon-induced distortion of crystal-field levels

New transverse field measurements on single crystal PrNi₅ have been carried out. The angular dependence of the Knight shift indicates ⁺ at f-sites of the hexagonal unit cell [(1/2 0 0), (0 1/2 0), (1/2 1/2 0)] in apparent contrast to previous conclusions. It is confirmed that the temperature dependence of the Knight shift does not scale with the bulk susceptibility. While the latter shows a distinct maximum around 15 K and Van Vleck behaviour for T0 K, the Knight shift does not exhibit any saturation down to 2 K. This peculiar behaviour is explained by a ⁺-induced change of the crystal field level scheme of the nearest-neighbour Pr³⁺-ions that significantly reduces the splitting between the lowest lying levels.     

Indication for a delocalized precursor μ+ state in CeAl3

The low temperature ( 0.6 K) ZF-SR signal in the heavy electron compound CeAl₃ displays a three component structure with one component revealing the precession of ⁺ in a static internal field of 220 G. Surprisingly the phase of this signal is shifted by the order of 90° which indicates the presence of a precursor state. The precursor state manifests itself by a quickly decaying nonoscillating component. A simple two state model with zero average field in the precursor state and 220 G in the final state can describe the results except for the magnitude of the phase shift.     

Muon depolarization in liquid3He

We report the first measurements of the positive-muon spin depolarization in liquid³He. The relaxation of the muon and muonium precession has been studied in transverse, longitudinal, and zero magnetic fields in the temperature range 0.5–2.5 K. The results are discussed in terms of two different depolarization mechanisms: recombinational depolarization (i.e. slow muonium formation) and magnetic relaxation due to the³He nuclear magnetic moments.     

α-Chlor-nitrone V: Substitutionsreaktionen an Olefin- und Benzolderivaten. Eine Methode zur Darstellung von β,γ-un-gesättigten und β- arylsubstituierten Aldehyden. Stereospezifische Bildung von tetra-alkylsubstituierten Olefindoppelbindungen. Über synthetische Methoden, 9. (vorläufige) Mitteilung

The Ag⁺-induced α-chloro-aldonitrone/olefin reaction in polar solvents can proceed by substitution, thereby providing a method for the preparation of β, γ-unsaturated aldehydes. Positional as well as configurational retention of the olefinic double bond are mechanistically significant and preparatively useful characteristics of this process. Substitution also occurs with great ease at nucleophilic aromatic nuclei; this offers a simple preparative route to certain β-aryl-aldehydes. The results illustrate a general aspect of the chemistry of α-chloro-aldonitrones: the N-alkenyl-N-alkyl-nitrosonium-ions derived from them can serve as preparative equivalents of the elusive corresponding α-acyl-carbonium-ions.