B. J. Sternlieb

Reduction of Ordered Moment and Néel Temperature of Quasi-One-Dimensional Antiferromagnets Sr2CuO3 and Ca2CuO3

We report elastic neutron diffraction and muon spin relaxation ({mu}SR) measurements of the quasi-one-dimensional antiferromagnets Sr{sub 2}CuO{sub 3} and Ca{sub 2}CuO{sub 3}, which have extraordinarily reduced T{sub N}/J ratios. We observe almost resolution-limited antiferromagnetic Bragg reflections in Sr{sub 2}CuO{sub 3} and obtain a reduced ordered moment size of {approximately}0.06{mu}{sub B}. We find that the ratio of ordered moment size {mu}(Ca{sub 2}CuO{sub 3})/{mu}(Sr{sub 2}CuO{sub 3})=1.5(1) roughly scales with their N{acute e}el temperatures, which suggests that the ordered moment size of quasi-one-dimensional antiferromagnets decreases continuously in the limit of vanishing interchain interactions. {copyright} {ital 1997} {ital The American Physical Society}

Static magnetic order in La1.875Ba0.125CuO4

Zero field muon spin relaxation measurements of high quality, single phase La1.875Ba0.125CuO4 indicate that this system exhibits static magnetic order below 38 K. At this x = 18 concentration, superconductivity is suppressed. The ordered spins most likely reside on the copper sites.

Quantum diffusion of muonium in GaAs

The diffusion rate of muonium in the III–V compound semiconductor GaAs has been determined from measurements of muon spinT1 relaxation induced by motion in the presence of nuclear hyperfine interactions. It is shown for the first time in a semiconductor that (a) there is a crossover of the transport mechanism at about 90 K from stochastic to zero-phonon hopping, as evidenced by a steep rise in the hop rate at lower temperatures, and that (b) the muonium diffuses at the hop rate of 1010 s−1 (corresponding diffusion constantD≈10−6 cm2s−1) at lower temperatures as well as at room temperature.

Positive muon Knight shift and spin relaxation in heavy fermion superconductors UPt3 and UBe13

Abstract We report muon spin rotation/relaxation (μSR) measurements of the heavy fermion superconductors UBe 13 and UPt 3 . In both materials we find that the muon Knight shift is unchanged in the superconducting state, consistent with odd-parity pairing (such as p-wave). The magnetic field penetration depths in UPt 3 and UBe 13 are extremely long, greater than 10000 A. We find no evidence of a magnetic transition in UBe 13 below 10 K.

Quantum diffusion of the positive muon in the superconducting state of Al

We report low temperature studies of muon diffusion and trapping in Al doped with Li impurities. The trapping rate at Li and the deduced muon diffusion rate increase more rapidly with decreasing temperature in the superconducting state compared with the normal state. The temperature dependence of the quantum diffusion rate in the superconducting state is close to that predicted by the Kondo theory.

Probing magnetism and superconductivity of high-Tc systems with positive muons

Abstract Recent results from our μSR experiments on high- T c systems are presented. We describe studies of static magnetic order in hole-doped and electron-doped systems, correlations between T c and n s / m * (carrier density / effective mass) in hole-doped superconducting cuprates, the temperature dependence of the penetration depth in c-axis oriented sintered ceramic of Y Ba 2 Cu 3 O 7 , as well as the detection of flux pinning phenomena by μSR.

Zero-field muon spin rotation studies in (TMTSF)2PF6

We report zero-field muon spin rotation studies of the organic compound (TMTSF)2PF6 at ambient pressure. An extremely sharp onset of the spin density wave state (SDW) is observed below the transition temperature TM = 12.2 K, which may be first order in nature. The saturation of the magnetic order at low temperatures can be ascribed to the existence of the SDW gap. The broad distribution of local magnetic fields deduced from μSR time spectra is consistent with that expected from an incommensurate SDW.

μ+ SR studies on Sr2CuO2Cl2, La2CuO4 and Nd2CuO4: 2-d magnetism, local fields and muon sitesSR studies on Sr2CuO2Cl2, La2CuO4 and Nd2CuO4: 2-d magnetism, local fields and muon sites

We compare the temperature dependence of the zero-field muon spin precession frequency observed in Sr2CuO2Cl2 and La2CuO4 below the Néel temperature with a 2-d Heisenberg model with an additional small anisotropy. Good agreement of the observed results with this model reflects the highly 2 dimensional magnetic properties of these cuprates. The measured local fields are compared with a simple calculation of dipolar fields in the crystal to search for muon site locations. Our results provide evidence that the muon sites are related to the oxygen atoms in these compounds.

Muon spin relaxation studies in frustrated and/or low-dimensional spin systems

An overview is given on muon spin relaxation (μSR) measurements in frustrated and/or low dimensional spin systems. In the frustrated Kagomé lattice system SrCr8Ga4O19, we observed dynamic spin fluctuations of ∼ 30 GHz, without any static frozen component even atT=0.1 K, much below the susceptibility-cusp temperatureTg=3.5 K. This is in clear contrast with the case in dilute-alloy spin glassesCuMn andAuFe, where static order develops belowTg. We also present the dimensionality dependence of the sub-lattice magnetization curves in 2-d Heisenberg systems, the remarkable suppression of the ordering temperature in a 1-d system Sr2CuO3, the observation of activation type spin dynamics in a 1-d Ising ferromagnet (DMeFc)(TCNE) aboveTc, slow spin fluctuations (∼ 60 MHz) in Haldane-gap systems at low temperatures, and some results from organic 1-d and 2-d magnetic systems.

Static magnetic order in electron-superconductor related compounds

Abstract Using the technique of muon spin relaxation, we have shown that the parent compounds Ln 2 CuO 4- y where [ Ln =( Nd , Sm or Pr )] of the new electron-superconductors exhibit static magnetic order below 300 K. No static magnetic order with any appreciable moment was observed above 4 K in superconducting samples of Nd 2- χ Ce χ CuO 4− y for χ > .155. Measurements on a single crystal of Nd 2 CuO 4− y show magnetic order with a sharp onset at 250 K, followed by a number of changes in the ordered spin direction at T ∼ 65 K and T ∼ 33 K.