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Abstract: Positive polarized muons act as non-destructive, non-invasive, and microscopic probes for local investigations. Over the years they have provided unique information about magnetic, superconducting and other electronic properties of bulk matter. A novel extension of the technique is given by the availability of with 100% spin polarization, and whose energy can be continuously varied from 0.5 to 30keV. This allows depth-dependent -studies of thin films, near-surface regions and multilayered structures in the range from to . After a brief introduction of the present status of this technique, some experiments are overviewed including depth-dependent studies of thin films and heterostructures of various magnetic and superconducting materials, ranging from cuprates through spin glasses to structures and compounds relevant to spintronics applications. [Copyright &y& Elsevier]

The muon is an elementary particle and, as such, forms a fundamental building block of the Standard Model of elementary particles. At the same time, the muon, especially the positively charged muon, when implanted in matter has established itself as a magnetic spin microprobe and hydrogen-like probe to study a variety of static and dynamic phenomena in superconductivity, magnetism, radical chemistry, semiconductor physics and many other fields. The limitation of this technique has been up until recently that it is restricted to investigation of bulk properties, because muons are generated from pion decay as high-energy particles with a broad stopping depth profile. This article describes recent developments of so-called 'slow muon' beams, where the energy is reduced down to the electronvolt to kiloelectronvolt range, thus making the probe depth sensitive on the nanometre scale. Some recent applications of this novel probe are described, such as the measurement of magnetic field profiles at the surface of superconductors and the measurement of the spatial variation in the polarization of conduction electrons in magnetic/non-magnetic multilayers. The generation of slow negative muons and possible applications of low-energy muons in the design of future muon colliders and neutrino sources are also briefly discussed. [ABSTRACT FROM AUTHOR]

In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds Sr2CuWO6 and Sr2CuMoO6 using magnetic susceptibility, muon spin rotation and relaxafion, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at Tmax = 83 and 95 K for Sr2CuWO6 and Sr2CuMoO6, respectively. However, three-dimensional long-range order takes place below TN = 24(1) and 28(2) K for Sr2CuWO6 and Sr2CuMoO6, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the ab plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the c axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearestneighbor interactions within the ab plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice. [ABSTRACT FROM AUTHOR]

The low energy muon (LEM) technique has been used to probe local changes in the dynamical spectrum of thin film polymer samples taking place as a function of the temperature and the implantation depth below the free surface. The studies have been made on samples of polydimethylsiloxane (PDMS) and polybutadiene (PB) using the transverse magnetic field (TF) configuration and diamagnetic probe muons. In PDMS evidence is found for suppression of the glass transition temperature near the surface, along with significantly modified dynamics in the near-surface region as well as at depths significantly below the surface. For PB the LEM technique reveals well-defined layers of dynamical and spatial inhomogeneity at depths of order 0.1–0.2 μ m below the free surface. These inhomogeneous regions may be assigned to nanopores produced by solvent streaming during preparation of spin-cast films. A thermal annealing procedure is shown to significantly reduce the thickness of these inhomogeneous layers. These results demonstrate that using LEM in the TF configuration provides a promising new method for studying surface-modified local dynamics of polymers that is also able to reveal nanostructured buried layers in polymer films. [ABSTRACT FROM AUTHOR]

The results of many experiments on polymers such as polystyrene indicate that the polymer chains near a free surface exhibit enhanced dynamics when compared with the bulk. We have investigated whether this is the case for poly(tetrafluoroethylene) (PTFE) by using zero-field muon-spin-relaxation spectroscopy to characterize a local probe, the F-Mu+-F state, which forms when spin-polarized positive muons are implanted in PTFE. Low-energy muons (implantation energies from 2.0 to 23.0 keV) were used to study the F-Mu+-F state between ~23 and 191 nm from the free surface of PTFE. Measurements were also made with surface muons (4.1 MeV) where the mean implantation depth is on the order of ~0.6 mm. The relaxation rate of the F-Mu+-F state up to ~ 150 K was found to be significantly higher for muons implanted at 2.0 keV than for higher implantation energies, which suggests that the polymer chains in a region on the order of a few tens of nanometers from the free surface are more mobile than those in the bulk. [ABSTRACT FROM AUTHOR]

The superconducting and magnetic properties of single crystalline (Li0.84Fe0.16)OHFe0.98Se with the transition temperature Tc≃40 K were studied by means of muon-spin rotation (μSR). The zero-field and field-shift μSR experiments confirm the homogeneity of the sample and the antiferromagnetic ordering within the (Li0.84Fe0.16)OH layers below Tm≃10 K. The temperature dependence of the in-plane component of the magnetic penetration depth (κab) was found to be consistent with gap opening within the superconducting FeSe planes, and it is well described within either the single s-wave gap or two s-wave gaps scenario. The opening of an additional small superconducting gap within the insulating (Li1-xFex)OH layers was detected from the temperature evolution of the out-of plane component of the magnetic penetration λ-2c(T). The superconductivity in (Li0.84Fe0.16)OH is most probably induced by the proximity to the superconducting FeSe layers. [ABSTRACT FROM AUTHOR]

The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 p 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs. [ABSTRACT FROM AUTHOR]