Field Muon Spin Relaxation Measurements Research Articles

Superconducting ground state of the nonsymmorphic superconducting compound Zr2Ir

The nonsymmorphic Zr$_{2}$Ir alloy is a possible topological semimetal candidate material and as such may be part of an exotic class of superconductors. Zr$_{2}$Ir is a superconductor with a transition temperature of 7.4 K with critical fields of 19.6(3) mT and 3.79(3) T, as determined by heat capacity and magnetisation. Zero field muon spin relaxation measurements show that time-reversal symmetry is preserved in these materials. The specific heat and transverse field muon spin rotation measurements rule out any possibility to have a nodal or anisotropic superconducting gap, revealing a conventional s-wave nature in the superconducting ground state. Therefore, this system is found to be conventional nonsymmorphic superconductor, with time-reversal symmetry being preserved and an isotropic superconducting gap.

Fast Spin Fluctuation Viewed by Muon Spin Relaxation in Optimally Doped and Overdoped Iron-Based Oxypnictide Superconductors LaFeAsO1-xFx

Zero field and longitudinal field muon spin relaxation measurements have been performed in optimally doped and overdoped superconductors LaFeAsO$_{1-x}$F$_x$ in order to investigate the magnetic fluctuation over a wide range of temperature and longitudinal field. We have observed no sign of magnetic fluctuation against temperature in the muons' time window (10$^{-5}\sim$ 10$^{-9}$s). Considering the current results and other results, i.e., spin fluctuation observed by neutron scattering, pseudogap-like behaviors by NMR and photoemission spectroscopy, it is suggested that not only the spin fluctuation but also the multiband character with several different orbital contributions at the Fermi surface may play an important role in the superconducting pairing mechanism of LaFeAsO$_{1-x}$F$_x$.

Direct Observation of the Ground-Spin Alignment of Fe(II)−Fe(III) Single-Chain Magnet by Muon-Spin Relaxation

Zero field and longitudinal field muon-spin relaxation measurements were carried out for the single-chain magnet catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4, to reveal the growth of short-range spin ordering in the zero-external magnetic field below 6 K.

Magnetic order in the quasi-one-dimensional spin-1∕2molecular chain compound copper pyrazine dinitrate

We present evidence of magnetic order in the quasi-one-dimensional spin-1/2 molecular chain compound, copper pyrazine dinitrate $\mathrm{Cu}({\mathrm{C}}_{4}{\mathrm{H}}_{4}{\mathrm{N}}_{2}){(\mathrm{N}{\mathrm{O}}_{3})}_{2}$. Zero field muon-spin relaxation measurements made at dilution refrigerator temperatures show oscillations in the measured asymmetry characteristic of a quasistatic magnetic field at the muon sites. Our measurements provide convincing evidence for long-range magnetic order below a temperature ${T}_{\mathrm{N}}=107(1)\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. This leads to an estimate of the interchain coupling constant of $\ensuremath{\mid}{J}^{\ensuremath{'}}\ensuremath{\mid}∕{k}_{\mathrm{B}}=0.046\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and to a ratio of $\ensuremath{\mid}{J}^{\ensuremath{'}}∕J\ensuremath{\mid}=4.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.

Observation of the spin-crossover in [Fe(btr) 2(NCS) 2] · H 2O (btr = 4,4′-bis-1,2,4-triazole) with μSR

The electronic spin transition in [Fe(btr) 2(NCS) 2] · H 2O (btr = 4,4′-bis-1,2,4-triazole) is probed by longitudinal field muon spin relaxation measurements. The μSR spectra could be analyzed with two different components, corresponding to two muon sites. For both components, an increase in magnetic fluctuations is observed at the LS → HS transition, i.e. crossing the spin transition temperature coming from low temperature, if a sufficiently high field is applied. Even below the transition temperature, magnetic fluctuations are still found. For one of the two muon sites, muonium formation is clearly found below the spin-crossover temperature.

A μ + SR study of ferromagnetic exchange in the fullerence charge transfer salt TDAE-C 60

Zero field muon spin relaxation measurements have been made on the charge transfer salt (tetrakisdimethylaminoethylene)C 60 [TDAE-C 60 ]. The effects of high temperature annealing on the dynamics and local magnetic properties of the compound are investigated. With the sample in the ferromagnetic α-phase, a signal characteristic of magnetic order is observed below 16 K. The initial asymmetry shows a discontinuity around 200 K, while the relaxation rate shows temperature activated behaviour above around 120 K. Annealing at 383 K is found to destroy the ferromagnetic signal and results in a relaxation rate peaked at 10 K, which may be attributable to the freezing out of a dynamic Jahn-Teller distortion.

Muon spin relaxation study ofLa1−xCaxMnO3

We report predominantly zero field muon spin relaxation measurements in a series of Ca-doped LaMnO_3 compounds which includes the colossal magnetoresistive manganites. Our principal result is a systematic study of the spin-lattice relaxation rates 1/T_1 and magnetic order parameters in the series La_{1-x}Ca_xMnO_3, x = 0.0, 0.06, 0.18, 0.33, 0.67 and 1.0. In LaMnO_3 and CaMnO_3 we find very narrow critical regions near the Neel temperatures T_N and temperature independent 1/T_1 values above T_N. From the 1/T_1 in LaMnO_3 we derive an exchange integral J = 0.83 meV which is consistent with the mean field expression for T_N. All of the doped manganites except CaMnO_3 display anomalously slow, spatially inhomogeneous spin-lattice relaxation below their ordering temperatures. In the ferromagnetic (FM) insulating La_{0.82}Ca_{0.18}MnO_3 and ferromagnetic conducting La_{0.67}Ca_{0.33}MnO_3 systems we show that there exists a bi-modal distribution of \muSR rates \lambda_f and \lambda_s associated with relatively 'fast' and 'slow' Mn fluctuation rates, respectively. A physical picture is hypothesized for these FM phases in which the fast Mn rates are due to overdamped spin waves characteristic of a disordered FM, and the slower Mn relaxation rates derive from distinct, relatively insulating regions in the sample. Finally, likely muon sites are identified, and evidence for muon diffusion in these materials is discussed.

A μSR study of the magnetic properties of CeAgSb 2

Zero and longitudinal field muon spin relaxation measurements have been performed on the Kondo lattice system CeAgSb 2 in the magnetically ordered ( T<10 K) and paramagnetic ( T>10 K) states. The resulting spectra are consistent with a single muon site which senses a unique coherent internal field of 53 mT at low temperatures and dynamic atomic fields, arising from extremely rapid RKKY-dominated paramagnetic fluctuations of the Ce 3+ spins, at higher temperatures. Small stepwise increases in the temperature dependence of the muon relaxation rate at 60 and 17 K appear to be coincident with the Kondo temperature and the onset of coherence, respectively.

Spin-labelling studies of benzene sorbed in carbon particles using muonium: a molecular view of sorption by environmental carbons

When benzene is sorbed into activated carbon powder, two distinct fractions are found using longitudinal field muon spin relaxation measurements, and are characterized by activation energies of 6 and 26 kJ mol−1 in respect of molecular reorientation. This is due to location of benzene in large (meso and macro) pores and micropores, respectively; escape from the latter is accompanied by a large, positive activation entropy of +52 J mol−1 K−1. Copyright © 2000 John Wiley & Sons, Ltd.

Probing the Spin-Spin Dynamical Autocorrelation Function in a Spin Glass above Tg via Muon Spin Relaxation.

We report zero and longitudinal field muon spin relaxation measurements in the metallic spin glass AgMn(0.5 at. %) at $Tg{T}_{g}$. We find that muon polarization obeys a time-field scaling relation which allows us to distinguish between three possible forms of the spin-spin dynamical autocorrelation function: a power law, a stretched exponential, and a cutoff power law. We also discuss the evolution of the muon relaxation line shape as the temperature approaches ${T}_{g}$.

Zero Field Muon Spin Relaxation Study of the Low Temperature State inα-(BEDT-TTF)2KHg(SCN)4

Zero field muon spin relaxation measurements are reported for the low temperature magnetic phase of the organic metal (BEDT-TTF${)}_{2}$KHg(SCN${)}_{4}$. Steplike changes in the relaxation rate indicate two transitions; the first occurs around 12 K and is accompanied by a change in the shape of the relaxation function. A further increase in the relaxation rate occurs below 8 K. These changes signify the onset of an internal magnetic field distribution below the transition, which is assigned to a spin-density-wave (SDW) ordering with an estimated amplitude of $\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}{\ensuremath{\mu}}_{B}$ below 8 K. This very small value is consistent with the upper limits set by previous magnetic resonance studies and also with a simple mean field description of the SDW transition.

Zero-field μSR study of CeRu2Si2 heavy fermion compound

Zero — field muon spin relaxation measurements have been carried out on a high-quality single-crystal sample of the paramagnetic heavy-fermion compound CeRu2Si2 from 5K to 300K. The observed relaxation at each temperature was well fitted by a function described by the product of a Kubo-Toyabe type and an exponential one. The temperature dependence of the Kubo-Toyabe relaxation rate σZF shows an almost constant value (0.03 μs−1) which is comparable to the calculated linewidth due to nuclear dipole fields from99Ru and101Ru atoms assuming the possible μ+ stopping sites for the ThCr2Si2 structure. On the other hand, we observed an increase of the exponential relaxation rate λZF to a value of ∼- 0.02 μs−1 with decreasing temperature below about 100K. This suggests a contribution of Ce 4f moments.

Static magnetic order in La 1.875Ba 0.125CuO 4

Zero field muon spin relaxation measurements of high quality, single phase La 1.875Ba 0.125CuO 4 indicate that this system exhibits static magnetic order below 38 K. At this x = 1 8 concentration, superconductivity is suppressed. The ordered spins most likely reside on the copper sites.

Fluctuation of rare-earth atom magnetic moments in superconducting ceramics (Ho,Er)-Ba-Cu-O studied by μSR

Zero field muon spin relaxation measurements of the ceramic high-Tc superconductors HoBa2Cu3O7-σ, Oc≃93 K) and ErBa2Cu3O7-σ (Tc≃95 K) reveal the sharp difference between the behaviours of the muon spin relaxation rate at temperatures below 20K. This fact may be explained by assumption that the frequency of fluctuations of Er magnetic moments exceeds by far the fluctuation frequency of Ho in 1-2-3 compounds.