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The muon-spin-relaxation (\ensuremath{\mu}SR) technique has been used to study the internal field modulation dynamics of fluxons in crystals of \ensuremath{\kappa}-[BEDT-TTF${]}_{2}$Cu[NCS${]}_{2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}10.5 K). The data exhibit a strong field dependence for applied fields in the range 129 Oe\ensuremath{\le}\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}\ensuremath{\le}4 kOe, which is attributed to a combination of vortex motion, finite core size effects, and pinning. In low fields (\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}=129 Oe), the data exhibit a flux-pinning transition at ${\mathit{T}}_{\mathit{x}}$\ensuremath{\sim}5 K, as evidenced by a peak in the second moment of the local field distribution at \ensuremath{\sim}5 K accompanied by an enhanced minimum in the first moment at the same temperature. In higher fields (\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}=750 Oe, 3 kOe, and 4 kOe), where the effects of motion and pinning are minimized, the symmetry of the underlying gap function is confirmed as s wave. Corrections for finite fluxon core, finite mean free path, and flux-lattice disorder were applied in determining the London penetration depth, ${\ensuremath{\lambda}}_{\mathit{L}}^{(\mathit{b}\mathit{c})}$(0)=7680\ifmmode\pm\else\textpm\fi{}700 \AA{}.

The ionization of muonium centers in Si and GaAs have been studied using radio frequency (RF) resonant techniques. In Si all three muonic centers are detectable by RF. No evidence was found for delayed Mu and Mu* states at any temperature. However, our results on the diamagnetic final state (μ f + ) show that it is composed of prompt fractions (as seen by conventional μSR) and delayed fractions arising from the ionization of Mu* and Mu. We observe a full μ f + fraction at 317 K when the Mu relaxation rate is above 10 μs−1. GaAs differs from the situation in Si in that we observed only a partial conversion of Mu* and Mu to a μ+ final state up to 310 K in spite of the fact that the transverse field relaxation rates become very high at 150 and 250 K respectively.

Ambient and high temperature X-ray diffraction methods were used to determine the unit cell parameters of the orthorhombic and tetragonal phases of the YBa2Cu3Ox compound, as a function of oxygen stoichiometry and temperature. The total oxygen content was obtained by the thermogravimetric method (TGA) by determining the weight loss in hydrogen up to 1000 degrees C. Reduction reactions in hydrogen were also performed in situ using a high temperature X-ray unit. Using the TGA method the oxygen content in the structure was obtained by weight loss in 100% oxygen. Thermal expansion coefficients of the lattice parameters were determined for both orthorhombic and tetragonal materials with different, constant x values.

We report a study of the organic compound $(TMTSF)_2 ClO_4$ in both a sample cooled very slowly through the anion ordering temperature (relaxed state) and a sample cooled more rapidly (intermediate state). For the relaxed state the entire sample is observed to be superconducting below about T_c ~ 1.2 K. The second moment of the internal field distribution was measured for the relaxed state yielding an in-plane penetration depth of ~ 12000 Angstroms. The intermediate state sample entered a mixed phase state, characterized by coexisting macroscopic sized regions of superconducting and spin density wave (SDW) regions, below T_c ~ 0.87 K. These data were analyzed using a back-to-back cutoff exponential function, allowing the extraction of the first three moments of the magnetic field distribution. Formation of a vortex lattice is observed below 0.87 K as evidenced by the diamagnetic shift for the two fields in which we took intermediate state data., Comment: 6 pages, 3 figures, to be submitted to Physica C

X-ray diffraction and thermogravimetric (TGA) studies have been carried out on orthorhombic YBa2Cu3Ox samples obtained by the reoxygenation of tetragonal samples. Thermogravimetric measurements performed in 100% oxygen provided data for the oxygen content (x) on the CuO basal planes. At fixed x higher than 6.8, samples obtained by different final heat treatments show different amounts of orthorhombic distortion (higher values for samples with higher degree of ordering). The orthorhombic distortion and oxygen content data have been used for the estimation of fractional site occupancy of O(1) and O(5) sites ∗ of YBa2Cu3Ox on the basis of Bakker's et al. 8theory. Differences in fractional site occupancy are obtained for samples with different degree of ordering.

The magnetic field penetration depth λ in single‐crystalline UPt3 has been measured by muon spin relaxation ( μ+SR). The temperature dependence of λ−2 is nonexponential and anisotropic decreasing from its T=0 value proportional to T when measured perpendicular to the c axis but with a higher‐power ∥c. Our data can be accounted for in detail by a superconducting gap with a line of nodes in the basal plane and axial point nodes. By neutron scattering we furthermore show that the antiferromagnetic order parameter of UPt3 is perturbed by the development of superconductivity. We discuss the implications of these results on the symmetry of the superconducting states of UPt3.

The satellites to the main aluminium resonance have been used to obtain information for up to fourth neighbours of the impurity. The principal axis directions have been determined. An anisotropy has been observed in the Knight shift at the nearest neighbours in AlMn which cannot be ascribed to a second rank tensor. The nearest neighbour Knight shift in AlCr was found to be isotropic and essentially temperature independent.

Dilute alloys of aluminium with gallium, silicon, germanium and magnesium, respectively, have been studied. The satellites to the main aluminium resonance have been used to obtain information about the electric field gradients due to a single impurity atom at neighbouring aluminium nuclei. Satellites due to nuclei which are as distant as fifth nearest neighbours to the impurity have been identified. For the magnesium alloy, the wipeout number for some satellites has been measured and has been found to be less than that for the main line.

NMR techniques have been used to determine the transition temperature for the onset of the charge density wave state in 2H-NbSe2 as a function of the residual resistance ratio of the samples. Within the framework of the chosen model, an ultimate transition temperature of 43K is determined for a sample with infinite residual resistance ratio and a critical resistance ratio of 12 below which the charge density wave state does not exist.

Muon-spin-rotation ({mu}{sup +}SR) studies of Bi{sub 2}Sr{sub 3{minus}{ital x}}Y{sub {ital x}}Cu{sub 2}O{sub 8+{ital y}} ({ital x}=0.3, 0.5, 0.6, 0.8, and 1.0) show that the magnetic ordering temperature {ital T}{sub {ital N}} falls rapidly with increasing hole concentration from {ital T}{sub {ital N}}(x=1.0)=210 K to {ital T}{sub {ital N}}(x=0.6)=10 K. In field-cooled high-field measurements Bi{sub 2}Sr{sub 2.7}Y{sub 0.3}Cu{sub 2}BO{sub 8+{ital y}} was found to be superconducting with {ital T}{sub {ital c}}{approx}65 K. The resulting phase diagram reflects a transition from magnetic to superconducting phases with increasing hole concentration similar to that found in studies of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} and La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4+{ital y}}.

Muon-spin rotation measurements have been performed on insulating samples of Y-doped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{x}$. In ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Y}{\mathrm{Cu}}_{2}{\mathrm{O}}_{x}$ muon-spin precession frequencies have been observed in zero applied field which are attributed to antiferromagnetic ordering, probably in the Cu${\mathrm{O}}_{2}$ planes. The transition is broad with an ordering temperature of about 210 K. ${\mathrm{Bi}}_{2}\mathrm{SrYCa}{\mathrm{Cu}}_{2}{\mathrm{O}}_{x}$ appears to be a disordered magnetic system with a spin-freezing temperature of 15 K. These results establish that there are strong magnetic correlations in the Bi 2:2:1:2 phase which are analogous to those observed previously in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ and $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$.

The transition temperatures from the normal to the superconducting state (Tc) of the high Tc superconducting compound YBa2Cu3Ox, have been measured by means of the four probe method. The oxygen content x has been determined with a thermogravimetric technique. The lattice parameters a, b, and c have been obtained on the basis of the x-ray powder diffraction spectra. At fixed x higher than 6.8, for samples obtained by the different final heat treatment, differences in Tc and in the unit cell parameters are observed. These differences indicate a dependence of Tc on ordering of the oxygen atoms and oxygen vacancies in the Cu-O basal plane and on sintering temperatures (Ts) at x=const..

A proof-of-principle experiment is presented demonstrating the generation of both direct and indirect spin echoes for ${\ensuremath{\mu}}^{+}$-spin spectroscopy. These two phenomena have direct bearing on several fundamental concerns, e.g., (i) muon diffusion and (ii) site determination in multinuclear systems. Also, in contrast to the case commonly found NMR, we conclude that the echo does not occur at $2{t}_{\ensuremath{\pi}}$ for a muon undergoing diffusive motion.

A nuclear magnetic resonance study of 115In in a single crystal of InBi has enabled the direct determination of the isotropic and anisotropic Knight shifts as well as the quadrupole interaction over the temperature range between 1.2 K and room temperature. An essentially linear variation with temperature is obtained for all three parameters with both the quadrupole interaction and the isotropic Knight shifts undergoing sign reversals in this temperature range. Comparisons are made with earlier nmr and time differential perturbed angular correlation (TDPAC) studies as well as with band structure predictions.

Zero- and longitudinal-field muon-spin relaxation μ+SR measurements have been performed on La_(2-x)Sr_xCuO_4 alloys in both single-crystal and sintered powder forms above and below their magnetic transition temperatures, T_f. The μ+ precession frequency v depends only weakly on x and T_f, an observation which together with resistivity data implies classical freezing of magnetic moments in the regime where the carriers are localized. For x=0.05, critical dynamics are observed near T_f. The μ^+SR technique is shown to be very sensitive to ferromagnetically aligned pairs of Cu^(2+) moments; the population of such pairs increases greatly with x.

Neutron scattering and muon spin relaxation studies of some materials related to high-T c superconductors are described. For La 2− x Sr x Cu O 4 with x as large as 0.05, our data indicate spin glass greezing with a frozen local moment of the same size as in the nominally pure(x=0) antiferromagnet. Magnetic fluctuations similar to those for La 2 Cu O 4 are found for La 2 Ni O 4 , which thus far has not been shown to be the parent compound of a superconductor.

StroboscopicμSR and TD-μSR techniques were used to measure theμ + Knight shiftK μ, and relaxation rateλ inSbBi alloys as functions of magnetic fieldH, temperatureT, the angleθ betweenH and the crystallineĉ axis, and the concentration [Bi] of alloyed Bi. In pure Sb and inSbBi (6.5%),K μ (θ=0) andK μ (θ=π/2) both decrease linearly withT up to about 100 K, but bothK μ and its anisotropy are smaller in the 6.5% alloy, indicating a “dilution” effect. With 15 at % Bi,K μ is reduced further but itsT-dependence and that ofλ are dramatically altered. At low temperaturesK μ (θ=0) inSbBi(15%) actually becomes negative and the sign of the anisotropy is reversed. In the same sample,λ is proportional toH at both 20 K and 150 K; at 120 Kλ is proportional toK μ ifθ is used as an implicit variable, but at 36 K this is not the case. A consistent phenomenological description is offered.

For Pt. I see abstr. A1732 of 1972. The electric field gradients at nearest and in some cases next nearest host Cu nuclei to various impurities in dilute Cu alloy single crystals have been determined by the quadrupole effects in nuclear magnetic resonance. The impurities are In, Sn, Sb and Ge. The field gradients at nearest neighbour sites are far from rotational symmetric around the direction towards the impurity and in the case of CuGe it does not even have the main component in that direction. These results question the validity of the theoretical models assuming spherical symmetry for the charge density around the impurity, at least in host metals like copper.

A study of the nuclear magnetic resonance spectrum of single crystals of three alloys of aluminium containing 0.5 at% Mg, Ga and Ge impurities respectively has revealed the presence of weak satellite lines whose dependence upon the orientation of the crystal in the magnetic field establishes that they originate at host sites which are nearest neighbours to the impurity. The Ga and Ge results contradict the earlier interpretation of Minier based upon pure quadrupole resonance studies and the new assignment is in greatly improved agreement with the theoretical calculations of Fukai and Watanabe.

A high resolution point detector geometry has been applied to the study of the angular correlation spectra from positron annihilation in Cu85Zn15 single crystals. Strong anisotropies are observed and some features are interpreted in terms of the alloy Fermi surface. A value for the [111] neck diameter is obtained which is 50% greater than that for pure copper. Considerable smearing of the expected slope discontinuity in the neighbourhood of the Fermi momentum is interpreted as evidence for Stern's theory of charging. A large anisotropy in the higher momentum contribution to the annihilation is also observed.

A point detector geometry with a resolution of 0.7 mrad. by 1.1 mrad. has been used to study the Fermi surface for several α phase alloys of Cu Ge. The variation of the [111] neck diameter and the [110] Fermi radius has been determined as a function of geranium concentration. Comparisons are made with previous work on this and other copper alloy systems, and also with the rigid band predictions.

The Knight shift Kμ at the positive muon has been measured as a function of magnetic field, temperature, crystal orientation and alloyed impurity (bismuth or tin) in antimony. The anomalously large and anisotropic Kμ in pure Sb at low temperature has been confirmed and shown to be independent of magnetic field up to 9 kG; its anisotropic part is found to have the same strong temperature dependence as its isotropic component. The addition of 6.3 at.% Bi significantly reduces both Kμ and its anisotropy, but enhances their temperature dependence. The addition of 12.5 at.% Bi, or, more dramatically, as little as 0.3 at.% Sn to antimony is sufficient to reduce Kμ to a small value, effectively eliminating the anomalous behaviour.

Positive-muon spin-rotation and -relaxation measurements of the oxygen-deficient perovskite YBa2Cu3O(x) have revealed local antiferromagnetic order for x = 6.0-6.4 with a Neel temperature TN that decreases rapidly with increasing oxygen content x. For slowly annealed samples with x = 6.35-6.5 the superconducting transition temperature Tc increases smoothly with x from 25 K at x = 6.348 to 60 K at x = 6.507. Two such samples with x = 6.348 and x = 6.400 appear to 'switch' from superconductivity to antiferromagnetic order at lower temperatures.

We report an improved measurement of the temperature dependence of the magnetic penetration depth in sintered YBa2Cu3O77 using muon spin rotation. The effective isotropic average of the magnetic penetration depth (λ) is estimated from the second moment of the field distribution in the vortex state in an external field of 15kG. The low temperature behaviour of λ is still consistent with an s-wave pairing mechanism although there are deviations from the conventional BCS-like behaviour for T/Tc > 0.2.

YBa2Cu3Ox is known to be antiferromagnetic (AFM) for x ≲ 6.45 but the details of its sublattice magnetization(s) are still controversial. A zero-field μ+SR investigation of the x- and T-dependence of the local fields at several muon sites reveals sharp changes at 10K and 80K for an oriented powder sample with x ≈ 6.0, but other x ≈ 6.0 samples do not show the same features. The direction of the local field at one μ+ site is shown to be along the ĉ-axis. For x < 6.0 the samples still show local spin freezing up to 300K, but coherent AFM order is lost even at 3K.

Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La2CuO(4-y) are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.

Resistivity, susceptibility and μ + SR measurements have been used to investigate the ( x , T ) phase diagram of YBa 2 Cu 3 O x . Carefully annealed samples are antiferromagnetic (AFM) insulators for 6.0 ≲ x ≲ 6.35 and nonmagnetic superconductors (SC) for 6.5 ≲ x ≲ 7.0; SC coexists with AFM or spin glass (SG) static magnetic order at low temperatures for 6.38 ≲ x ≲ 6.48. A sample with x = 6.462 is SC below 25 K and simultaneously magnetic below 10 K; the internal diamagnetism of the SC state is progressively reduced as local spin freezing sets in at low temperatures.