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Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr_2Ir_2O_7 for temperatures in the range 0.025-250 K. Kubo-Toyabe relaxation functions are observed up to > 200 K, indicating static magnetism over this temperature range. The T -> 0 static muon spin relaxation rate Delta(0) ~ 8 mus^-1 implies a weak quasistatic moment (~0.1 mu_B). The temperature dependence of Delta is highly non-mean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero below ~150 K. The data rule out ordering of the full Pr^3+ CEF ground-state moment (3.0 mu_B) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced ^141Pr nuclear magnetism. The dynamic relaxation rate lambda increases markedly below ~20 K, probably due to slowing down of spin fluctuations in the spin-liquid state. At low temperatures lambda is strong and temperature-independent, indicative of a high density of low-lying spin excitations as is common in frustrated antiferromagnets., 4 pages, 3 figures, to appear in Proc. 11th Int. Conf. on Muon Spin Rotation, Relaxation and Resonance (muSR2008)

We report on detailed longitudinal field (LF) muon spin relaxation studies in SmRu 4 P 12 in order to characterize magnetic fluctuations in a magnetically ordered state below T MI = 16.5 K . The magnitude and fluctuation rate of the fluctuating field are derived as functions of temperature from LF dependence of the longitudinal relaxation rate. Possible low-energy excitations of magnetic multipoles are discussed.

Wide varieties of strongly correlated electron phenomena are performed on the stage of a “filled skutterudite structure”. Especially when one of the players contains a plural number of 4f electrons, the orbital degrees of freedom play a major role as a new type of nonmagnetic and/or weak-magnetic phenomena. Several examples found in Pr- and Sm-based filled skutterudites are introduced in relation to muon spin relaxation (μSR) experiments.

Zero field (ZF) and transverse field (TF) muon spin relaxation and rotation ( μ SR ) study has been carried out in filled-skutterudite SmOs 4 Sb 12 in order to investigate the magnetically robust heavy-fermion (HF) state and the weak ferromagnetic anomaly appearing below ∼ 2.5 K . A large-amplitude oscillating signal appears in the ZF- μ SR spectra at low temperatures, confirming that the weak ferromagnetic anomaly is an intrinsic bulk property. Two components with the fraction ratio of ∼ 2 : 1 exist both in the ZF- μ SR spectra of the ferromagnetically ordered state and the TF- μ SR FFT spectra in applied fields along the 〈 0 0 1 〉 direction. This observation can be explained consistently based on the most probable muon stopping site indicated from the value of the static nuclear dipolar width in Kubo–Toyabe function in the high-temperature ZF- μ SR spectra. Analysis reveals that the spontaneous magnetic moment M s lies along the 〈 0 0 1 〉 direction and the size of M s is largely suppressed, indicating that the weak ferromagnetic moment is carried by itinerant heavy quasiparticles.

The local magnetic state of SmRu4P12 in the possible octupole ordering phase was studied at 15 K by means of the zero field, longitudinal field, and transverse field muon spin rotation/relaxation methods. We observed that the internal field at each muon site consists of quasi-static and dynamical fields. A possible interpretation of the coexistent fields is discussed.

We have performed muon Knight shift measurements in the heavy-fermion compound ( Ce 1 - x La x ) 2 IrIn 8 , x = 0.1 , in 1 T magnetic field applied along the crystalline c -axis. Although the Knight shift K scales linearly with susceptibility χ above T ∼ 20 K , a breakdown of this relationship was observed below a temperature T * = 20.1 ( 8 ) K . It was found that this Knight shift anomaly occurs due to a low-temperature susceptibility component χ cf ∼ ( 1 - T / T * ) ln ( T * / T ) , corresponding to the formation of a coherent heavy-fermion state below T * , as found previously in the x = 0 compound. The characteristic temperature T * is reduced by about 4 K for 10% La doping, indicating a reduction in the strength of the intersite Ce fluctuations associated with the heavy electron state.

We review results from previous muon spin relaxation ( μ SR) measurements in applied fields of H 0 = 0 and 0.25 T which established an upper limit for the ordered or disordered frozen spin moment above T = 4 K in δ -Pu (4.3 at.% Ga) of μ ord ≤ 1 0 − 3 μ B . In addition, we present new data in H 0 = 0.25 and 2 T applied field on a highly annealed δ -Pu (4.3 at.% Ga) sample. Neither the muon Knight shift ( H 0 = 2 T) nor the inhomogeneous linewidths in the new sample show appreciable temperature dependence below about T = 60 K, also consistent with no spin freezing. Recent theoretical arguments advanced to explain these results are mentioned.

The penetration depth λ in the filled-skutterudite heavy-fermion superconductor PrOs4Sb12 has been measured using transverse-field muon spin rotation (TF- μ SR ). It is found to be temperature-independent at low temperatures, consistent with a nonzero gap for quasiparticle excitations. In contrast, radiofrequency (RF) measurements yield a stronger temperature dependence of λ ( T ) , indicative of point nodes in the gap. A ∼ 10 % discrepancy is found at low temperatures. This may be due to mechanisms that modify the vortex-state field distribution, or to the surface scattering which breaks pairs in an odd-parity superconductor. Alternatively, it may be a matter of field orientation of nodal gap structure in the μ SR measurements.

We present the first μ SR measurements ever performed on elemental Pu, and set the most stringent upper limits to date on the magnitude of the ordered moment μ ord in α -Pu and δ -stabilized Pu (alloyed with 4.3 at% Ga). Assuming a nominal hyperfine coupling field of 1 kOe/ μ B we find μ ord ⩽ 10 - 3 μ B at T ≅ 4 K .

We present transverse-field (TF) measurements of the in-plane magnetic-field penetration depth λ ( T ) in single-crystalline PuCoGa 5 ( T c = 18.5 K ) for 0.06 T applied field ( ≈ 2 – 5 × H c 1 ) . We find that the temperature dependence of the superfluid density, and therefore Δ λ ( T ) = λ ( T ) - λ ( 0 ) , is ∝ T for T / T c ⩽ 0.5 . We estimate that the measured λ ( 0 ) = 241 ( 3 ) nm . ZF measurements find no evidence for time-reversal symmetry violation. The ZF and TF measurements are consistent with an even-parity (pseudo-spin singlet), d-wave pairing state.

We present recent measurements of the magnetic properties of Pu metal and the superconducting properties of PuCoGa 5 using the µSR technique. Our measurements set the most stringent upper limits to date on the magnitude of the ordered moments µ ord in α-Pu and δ-stabilized Pu (alloyed with 4.3 at. % Ga) in zero applied field: µ ord ≤10 -3 µ B at T \cong4 K. Measurements of the in-plane magnetic-field penetration depth λ( T ) in PuCoGa 5 ( T c =18.5 K) for 0.06 T applied field (≈2-5 × H c1 ) show that the temperature dependence of the superfluid density, and therefore Δλ( T )=λ( T )-λ(0), are ∝ T for T / T c ≤0.5. We estimate that λ(0)=241(3) nm. We also find no evidence for a time-reversal-symmetry violating superconducting order parameter. Taken together the measurements in PuCoGa 5 are, therefore, consistent with an even-parity (pseudo-spin singlet), d-wave pairing state.

A study of the effects of Bragg peak profiles and nanoparticle size broadening on the real-space pair distribution function (PDF) is presented, using `synthetic' powder diffraction data. Bragg peak profiles from both asymmetric time-of-flight (TOF) spallation neutron data and symmetric synchrotron X-ray data are considered. Due to their asymmetric peak profiles, the TOF data cause artificial shifts of the PDF peak positions towards higher pair distances. Coupled with this effect is a broadening of the PDF peak widths due to aQ-dependent spectrometer resolution, making reliable refinement of thermal parameters difficult. These effects become more pronounced as theQresolution becomes worse. By contrast, the symmetric X-ray powder diffraction data do not cause a systematic shift of the PDF peak positions, and the broadening of the PDF peak widths has a relatively minor effect on the extraction of the thermal parameters. Finally, nanoparticle size broadening of the asymmetric neutron TOF powder diffraction data causes a shift of the PDF peak positions towards lowerrvalues and smears the PDF intensities from one atomic shell to another.

We report a series of measurements in (La, Ca, Pr)MnO3 compounds which show that ferromagnetic (FM) CMR compounds develop two Mn-ion spin–lattice relaxation channels as the materials are cooled below their insulator-to-metal transition temperature TMI. This result is in contrast to conventional FMs and is attributed to the presence of both insulating and conducting FM regions below TMI which coexist on a microscopic scale. The coexistence of different phases is found in both polycrystalline and single-crystalline materials, though the single crystal exhibits a narrower temperature region of phase coexistence below its FM critical temperature TC. Possible differences between crystalline and granular materials which could give rise to these findings are discussed. These results could have important implications for the use of CMR materials in spintronics devices, which rely on conducting surfaces in thin film multilayers below TC.

A spectrometer for β-detected nuclear magnetic resonance (β-NMR) has been commissioned at the ISAC facility at TRIUMF. A beam of low energy highly spin polarized 8Li+ can be decelerated and implanted into ultra-thin structures 6–400 nm thick. β-NMR provides local information on the electronic and magnetic properties of materials which is similar to conventional NMR but can be used as a sensitive probe of ultra-thin films, interfaces and other nanostructures. We report here on the status of the spectrometer and preliminary results on a simple metal film.

Magnetic resonance (muSR and NMR) studies of f-electron non-Fermi-liquid (NFL) materials give clear evidence that structural disorder is a major factor in NFL behavior. Longitudinal-field muSR relaxation measurements at low fields reveal a wide distribution of muon relaxation rates and divergences in the frequency dependence of spin correlation functions in the NFL systems UCu_{5-x}Pd_x and CePtSi_{1-x}Ge_x. These divergences seem to be due to slow dynamics associated with quantum spin-glass behavior, rather than quantum criticality as in a uniform system, for two reasons: the observed strong inhomogeneity in the muon relaxation rate, and the strong and frequency-dependent low-frequency fluctuation observed in U(Cu,Pd)_5 and CePt(Si,Ge). In the NFL materials CeCu_{5.9}Au_{0.1}, Ce(Ru_{0.5}Rh_{0.5})_2Si_2, CeNi_2Ge_2, and YbRh_2Si_2 the low-frequency weight of the spin fluctuation spectrum is much weaker than in the disordered NFL systems., 10 pages, 4 figures. To be published in proceedings of muSR2002 (Physica B)

We report μ + -Knight shift measurements as a function of temperature in U 1− x Th x Be 13 , x =0 and 0.035, single crystals. An anomalous change in the hyperfine coupling at low temperatures is observed which is similar to that reported in nuclear magnetic resonance studies of U- and Ce-based heavy fermion compounds. In the superconducting phase the static spin susceptibility, χ spin , determined from the μ + -Knight shift decreases continuously with decreasing temperature in pure UBe 13 , but saturates below the second transition temperature in U 0.965 Th 0.035 Be 13 . We briefly discuss these behaviors in terms of a two-component spin-triplet order parameter and propose μSR experiments that can test our hypothesis.

Colossal magnetoresistance manganites are archetypes in which to study the strong coupling between spin, charge and lattice degrees of freedom in materials. We present muon spin-lattice relaxation data in ferromagnetic (FM) ground state materials from the manganite series La 1-x Ca x MnO 3 and La 1-x-y Pr y Ca x MnO 3 . These measurements reveal several characteristic relaxation modes arising from the strong spin-charge-lattice interactions. We also present results from neutron-spin-echo spectroscopy, which directly measures the spin-spin correlation function in a time domain comparable to μSR. A qualitative model for the FM transition in the manganites involving microscopic phase separation is suggested by these data.

We have commissioned a polarized low-energy 8 Li ion beam line, which together with a high-field β-NMR spectrometer, can act as sensitive new probe of thin films and interfaces. The implantation energy can be continuously adjusted from 1 to 90 keV and the maximum polarization achieved thus far is 80%. This instrument opens up new applications for β-NMR which parallel and complement efforts with low-energy muons. For example, it is possible to probe the magnetic field distribution near the surface of a material by stopping a polarized 8 Li beam in a thin overlayer of Ag. Since the 8 Li adopts a site with cubic symmetry in Ag there is no quadrupolar splitting of the resonance, and the 8 Li acts as a purely magnetic sensor.

The series of intermetallic compounds RE 5 Ir 4 Si 10 (RE=rare-earth) shows unusual charge density wave (CDW) order for temperatures lower than 160 K . This work presents a muon spin rotation (μSR) study, in zero external field, on single crystalline samples of the magnetic Er 5 Ir 4 Si 10 ( T CDW =155 and 55 K ) and polycrystalline samples of Er 5 Ir 4 Ge 10 (no CDW). The muon relaxation rate λ is strongly temperature dependent in both compounds. Furthermore, upon cooling below the CDW transition temperatures, a kink is seen in λ in Er 5 Ir 4 Si 10 . We interpret this result as a signature of the change in the density of states due to the establishment of the CDW.

For some time now, there has been considerable experimental and theoretical effort to understand the role of the normal-state “pseudogap” phase in underdoped high-temperature cuprate superconductors. Recent debate has centered on the question of whether the pseudogap is independent of superconductivity. We provide evidence from zero-field muon spin relaxation measurements in YBa 2 Cu 3 O 6+ x for the presence of small spontaneous static magnetic fields of electronic origin intimately related to the pseudogap transition. Our most significant finding is that, for optimal doping, these weak static magnetic fields appear well below the superconducting transition temperature. The two compositions measured suggest the existence of a quantum critical point somewhat above optimal doping.

We report new zero-field muon spin relaxation and neutron spin echo measurements in ferromagnetic (FM) (La,Ca)MnO3 which suggest at least two spatially separated regions possessing very different Mn-ion spin dynamics. One region displays diffusive relaxation, "critical slowing down" near T(C) and an increasing volume fraction below T(C), suggesting overdamped FM spin waves below T(C). The second region possesses more slowly fluctuating spins, a linewidth independent of q, and a decreasing volume fraction below T(C). The estimated length scale for the inhomogeneity is

We report new zero-field μSR measurements in ferromagnetic (FM) (La,Ca)MnO3 which are consistent with two spatially separated regions in close proximity possessing very different Mn-ion spin dynamics. We present a picture in which one region corresponds to an extended spin polaron which displays a peak in the relaxation rate near the Curie temperature TC and an increasing volume fraction below TC. The second region possesses slower fluctuating spins and a decreasing volume fraction below TC. These data suggest a microscopically inhomogeneous FM phase transition resulting from the overlap of spin polarons.

We report muon spin rotation measurements of the temperature dependence of the μ+-Knight shift in single crystals of UBe13. The dipolar fields produced by the uranium 5f-electron moments result in two magnetically inequivalent μ+ sites. Below Tc, the magnitude of the Knight shift is observed to decrease with decreasing T at one of the sites, whereas it is found to increase at the other site. The data is explained by an effective exchange interaction between the μ+ and the 5f-electrons which is temperature dependent and anisotropic below T≈6 K.

Muon spin relaxation measurements of the magnetic field penetration depth λ have been performed in a quasi two-dimensional (2-d) superconductor based on HfNCl intercalated with Li and organic molecules. The relaxation rate σ(T→0)∼0.5 μs −1 was obtained with transverse fields applied perpendicular to the aligned HfN planes. Using the relation σ∝λ −2 ∝n s2d /m ∗ (2-d superconducting carrier density/effective mass), we deduced the 2-d Fermi temperature TF2d. The ratio Tc/TF2d for the HfNCl-(Li) system is very close to those in two other quasi-2-d superconductors, YBa2Cu3O7 and (BEDT-TTF)2-X. Compared to the Kosterlitz–Thouless (KT) transition temperature TKT=TF2d/8 for the limit of strong coupling, Tc's of these systems are reduced by a factor of 3–4, indicating the importance of carrier overlapping and/or 3-d coupling.

The geometrically frustrated spin-glass Y{sub 2}Mo{sub 2}O{sub 7} has been widely considered to be crystallographically ordered with a unique nearest-neighbor magnetic exchange interaction, J. To test this assertion, we present x-ray-absorption fine-structure results for the Mo and Y K edges as a function of temperature and compare them to results from a well-ordered pyrochlore, Tl{sub 2}Mn{sub 2}O{sub 7}. We find that the Mo-Mo pair distances are significantly disordered at approximately right angles to the Y-Mo pairs. These results strongly suggest that lattice disorder nucleates the spin-glass phase in this material. (c) 2000 The American Physical Society.

We report zero-, longitudinal-, and transverse-field positive muon spin relaxation ({mu}SR) measurements in single crystals of the heavy-fermion superconductor UBe{sub 13} [T{sub c}=0.83(2) K]. Our zero-field measurements provide an upper limit for any quasistatic magnetic moments in this system below 100 K of 0.001{mu}{sub B}, consistent with previous measurements on polycrystals. From the transverse-field measurements we find a lower bound for the London penetration depth {lambda}{sub L}=1210 nm. This value implies a lower limit for the effective mass consistent with the low-temperature specific heat. (c) 2000 The American Physical Society.

Muon spin relaxation experiments have been carried out in the Kondo compound ${\mathrm{PrInAg}}_{2}.$ The zero-field muon relaxation rate is found to be independent of temperature between 0.1 and 10 K, which rules out a magnetic origin (spin freezing or a conventional Kondo effect) for the previously observed specific-heat anomaly at $\ensuremath{\sim}0.5 \mathrm{K}.$ At low temperatures the muon relaxation can be quantitatively understood in terms of the muon's interaction with nuclear magnetism, including hyperfine enhancement of the ${}^{141}\mathrm{Pr}$ nuclear moment at low temperatures. This argues against a ${\mathrm{Pr}}^{3+}$ ground-state electronic magnetic moment, and is strong evidence for the doublet ${\ensuremath{\Gamma}}_{3}$ crystalline-electric-field-split ground state required for a nonmagnetic route to heavy-electron behavior. The data imply the existence of an exchange interaction between neighboring ${\mathrm{Pr}}^{3+}$ ions of the order of 0.2 K in temperature units, which should be taken into account in a complete theory of a nonmagnetic Kondo effect in ${\mathrm{PrInAg}}_{2}.$

Zero field (ZF) and transverse field (TF) muon spin relaxation and rotation ( μ SR ) experiments have been carried out in the Cd-doped heavy fermion superconductor CeCoIn 5 to investigate its superconducting state. The ZF- μ SR results in CeCo ( In 0.97 Cd 0.03 ) 5 revealed that no spontaneous magnetic field was induced below its superconducting transition temperature ( T c ), indicating no evidence for time reversal symmetry breaking. The muon Knight shifts obtained from TF- μ SR measurements decrease significantly below T c , consistent with a spin-singlet state as in the parent compound CeCoIn 5 , which is a d-wave superconductor.

The Japan Atomic Energy Agency (JAEA)-Advanced Science Research Center (ASRC) is advancing a “μSR project” at the J-PARC MLF muon science facility (MUSE). This project entails extracting part of the muon beam into a muon spectrometer constructed downstream from the Decay/Surface muon beam line. One of the main subjects of study at the ASRC μSR project will be an examination of strongly correlated electron systems, especially f-electron systems. The intense muon beams available at MUSE will yield new insights for f-electron physics.

A novel high magnetic field (8 T) spectrometer for muon spin rotation has been used to measure the temperature dependence of the in-plane magnetic penetration depth {lambda}{sub ab} in YBa{sub 2}Cu {sub 3}O{sub 6.95} . At low H and low T , {lambda}{sub ab} exhibits the characteristic linear T dependence associated with the energy gap of a d{sub x{sup 2}-y{sup 2}}-wave superconductor. However, at higher fields {lambda}{sub ab} is essentially temperature independent at low T . We discuss possible interpretations of this surprising new feature in the low-energy excitation spectrum. (c) 1999 The American Physical Society.

We performed muon Knight shift measurements on randomly aligned single crystalline samples of SmRu 4 P 12 in a magnetic field of 6 T. A marked increase in the muon spin relaxation rate was observed below a metal-insulator transition temperature, interpreted as an occurrence of finite local fields due to a dipole and/or octupole ordering. An expected magnetic anomaly at around 14 K in high fields was still obscure in a field of 6 T.

The effective superconducting penetration depth measured in the vortex state of PrOs 4 Sb 12 using transverse-field muon spin rotation ( TF - μ SR ) exhibits an activated temperature dependence at low temperatures, consistent with a nonzero gap for quasiparticle excitations. In contrast, Meissner-state radiofrequency (rf) inductive measurements of the penetration depth yield a T 2 temperature dependence, suggestive of point nodes in the gap. A scenario based on the recent discovery of extreme two-band superconductivity in PrOs 4 Sb 12 is proposed to resolve this difference. In this picture a large difference between large- and small-gap coherence lengths renders the field distribution in the vortex state controlled mainly by supercurrents from a fully gapped large-gap band. In zero field all bands contribute, yielding a stronger temperature dependence to the rf inductive measurements.

X-ray-absorption fine-structure measurements of the local structure in UCu{sub 4}Pd are described which indicate a probable lattice-disorder origin for non-Fermi-liquid behavior in this material. Short Pd-Cu distances are observed, consistent with (24{plus_minus}3){percent} of the Pd atoms occupying nominally Cu sites. A {open_quotes}Kondo disorder{close_quotes} model, based on the effect on the local Kondo temperature T{sub K} of this interchange and some additional bond-length disorder, agrees quantitatively with previous experimental susceptibility data, and therefore also with specific heat and magnetic resonance experiments. {copyright} {ital 1998} {ital The American Physical Society }

Muon spin rotation experiments on a stoichiometric sample of the non-Fermi-liquid (NFL) heavy-fermion compound ${\mathrm{UCu}}_{4}\mathrm{Pd},$ in which recent neutron scattering experiments suggest an ordered structure, indicate that the U-ion susceptibility is strongly inhomogeneous at low temperatures. We argue that this is due to residual disorder, which also dominates NFL behavior. The data yield a short correlation length ($\ensuremath{\lesssim}1$ lattice spacing) and a rapid low-temperature U-moment relaxation rate $(\ensuremath{\gtrsim}{10}^{12}{\mathrm{s}}^{\mathrm{\ensuremath{-}}1}),$ which constrain cluster-based models of NFL behavior.

Muon spin relaxation experiments in the geometrically frustrated antiferromagnet NiGa 2 S 4 indicate strong slow spin fluctuations at low temperatures. The muon relaxation rate is strongly field dependent, in contrast with the field independence of the gapless excitations indicated by the observed specific heat.

Freshly prepared samples of PuCoGa 5 have the highest superconducting critical temperature T c ≅ 19 K of all f-electron superconductors. In addition, this material undergoes self-irradiation from the radioactive decay of the Pu nuclei. We report muon spin rotation ( μ SR ) measurements of the superconducting penetration depth λ in 400 day-old single crystalline samples of PuCoGa 5 ( T c ≅ 15.5 K ) , and compare these results to μ SR measurements taken on the same samples after only 25 days of aging ( T c ≅ 18.5 K ) , in order to elucidate the symmetry of the order parameter and its dependence on aging. The experiments show that the low-temperature superfluid density n s decreases linearly with increasing T in both fresh and aged PuCoGa 5 , consistent with a line of nodes in the order parameter.

We performed muon spin rotation and relaxation measurements on a single crystalline sample of PrPb 3 in a magnetic field H ∥ [ 0 0 1 ] from 100 down to 2.5 K . A quite anisotropic contact-coupling constant was extracted from the muon Knight shift, possibly concerned with nonspherical distribution of 4f-electron at low temperature. The contact and dipole coupling constants are of comparable magnitudes, suggesting strong hybridization between the 4f electrons of Pr and the conduction electrons.

Zero-field muon spin relaxation ( μ SR ) experiments have been carried out in the Pr ( Os 1 - x Ru x ) 4 Sb 12 and Pr 1 - y La y Os 4 Sb 12 alloy systems to investigate the time-reversal symmetry (TRS) breaking found in an earlier ZF- μ SR study of the end compound PrOs 4 Sb 12 . Our results suggest that Ru doping is considerably more efficient than La doping in suppressing TRS-breaking superconducting pairing in PrOs 4 Sb 12 .

We present zero-field muon spin relaxation (\ensuremath{\mu}SR) measurements of ${\mathrm{La}}_{1.6\ensuremath{-}x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ with $x=0.125,0.15,0.2;{\mathrm{La}}_{1.475}{\mathrm{Nd}}_{0.4}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_{4},{\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_{4},$ and ${\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125\ensuremath{-}y}{\mathrm{Sr}}_{y}{\mathrm{CuO}}_{4}$ with $y=0.025,0.065.$ All of the samples with dopant concentrations $x+yl~0.15$ show similar static magnetic order with coherent precession of the muon spins below ${T}_{N}\ensuremath{\approx}30\mathrm{K},$ with a $\stackrel{\ensuremath{\rightarrow}}{T}0$ ordered Cu moment $\ensuremath{\approx}0.3{\ensuremath{\mu}}_{B}.$ The samples with $x=0.20$ show no coherent precession but manifest two distinct relaxation regimes, typical of quasistatic magnetism. We then present transverse-field \ensuremath{\mu}SR hysteresis measurements of the ${\mathrm{La}}_{1.45}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}$ and ${\mathrm{La}}_{1.4}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{0.2}{\mathrm{CuO}}_{4}$ systems that show a large superconducting response below approximately 7 K and 12 K, respectively. We argue that superconductivity and magnetic order coexist in the $x=0.15$ system.

We report zero-field muon spin rotation data in single crystals of La{sub 1.4}Sr {sub 1.6}Mn{sub 2}O{sub 7} for T=5{endash}325 K . The spin-lattice relaxation rate is spatially inhomogeneous below the 3D magnetic transition temperature T{sub C} and anisotropic above T{sub C} . We find evidence against 2D spin ordering or in-plane correlations above T{sub C} . Additionally, the very slow spin fluctuations found below T{sub C} in cubic (3D) perovskites like (La,thinspCa)MnO{sub 3} or (La,thinspSr)MnO{sub 3} , and attributed to relatively small magnetoelastic polarons, are absent in La{sub 1.4}Sr {sub 1.6}Mn{sub 2}O{sub 7} . This suggests that the polaron size in the layered material is significantly larger than in the 3D perovskites. {copyright} {ital 1998} {ital The American Physical Society}

Longitudinal-field muon spin relaxation (LF- μ SR) experiments have been performed in unannealed and annealed samples of the heavy-fermion compound UCu 4 Pd to study the effect of disorder on non-Fermi liquid behavior in this material. The muon spin relaxation functions G ( t , H ) obey the time-field scaling relation G ( t , H ) = G ( t / H γ ) previously observed in this compound. The observed scaling exponent γ = 0.3 ± 0.1 , independent of annealing. Fits of the stretched- exponential relaxation function G ( t ) = exp [ - ( Λ t ) K ] to the data yielded stretching exponentials K 1 for all samples. Annealed samples exhibited a reduction of the relaxation rate at low temperatures, indicating that annealing shifts fluctuation noise power to higher frequencies. There was no tendency of the inhomogeneous spread in rates to decrease with annealing, which modifies but does not eliminate the glassy spin dynamics reported previously in this compound. The correlation with residual resistivity previously observed for a number of NFL heavy-electron materials is also found in the present work.

Transverse-field μ SR shifts and relaxation rates have been measured in the non-Fermi liquid (NFL) alloy system UCu 5 - x Pt x , x = 1.0 , 1.5, and 2.5. At low temperatures the fractional spread in Knight shifts δ K / K ≈ δ χ / χ is ≳ 2 for x = 1 , but is only half this value for x = 1.5 and 2.5. In a disorder-driven scenario where the NFL behavior is due to a broadly distributed (Kondo or Griffiths-phase cluster) characteristic energy E , our results indicate that δ E / E av ≈ ( δ K / K ) T → 0 is similar for UCu 5 - x Pd x ( x = 1 and 1.5) and UCu 4 Pt, but is reduced for UCu 5 - x Pt x , x = 1.5 and 2.5. This reduction is due to a marked increase of E with increasing x ; the spread δ E is found to be roughly independent of x. Our results correlate with the observed suppression of other NFL anomalies for x > 1 in UCu 5 - x Pt x but not in UCu 5 - x Pd x , and are further evidence for the importance of disorder in the NFL behavior of both these alloy systems.

We report on muon spin rotation (µSR) measurements in PuCoGa 5 single crystals in a 400 day-old sample in order to investigate the self-irradiation (aging) effect. Compared with the results in 25 day-old sample, the µSR line widths in the 400 day-old sample are found to be anomalously narrow. It is considered that the narrowing of line width is caused by random defects, which are created by Pu disintegration, namely, vortex segments are pinned randomly and three-dimensionally by the defects.

Among the family encompassed by the complex metal oxides are the colossal magneto-resistive perovskites with potential applications in advanced high density magnetic data storage and sensor devices based on single or multilayers of these materials fabricated by vapor phase deposition methods. Realization of this potential requires solving basic thin film fabrication problems coupled to understanding the resulting structure-properties relationships. The specific objectives addressed in this study were to determine the dependence of growth and transport properties: (1) reproducibility on the pulsed laser deposition (PLD) target, (2) on sputter deposition chamber gas and substrate, and (3) on a post-deposition anneal in a reducing atmosphere. Toward these ends, we have grown La 0.67 Ca 0.33 MnO 3 films on perovskite substrates by PLD and RF off-axis sputter deposition from stoichiometric targets at temperatures from 400 to 900°C. The PLD films were grown from a new commercial target and post-deposition annealed in O 2 to reproduce, for comparison, the conditions used previously for the films grown with an in-house fabricated target. The sputter deposited films were grown in both ArO 2 mixed and Ar-only atmospheres, some grown simultaneously on different substrates; one ArO 2 grown film was post-annealed in a reducing atmosphere. Microstructures were studied by scanning probe microscopies and temperature-dependent transport properties by 4-point resistance measurements. Previously we reported on characterization of the T substrate ( T s )-dependent microstructure of PLD as-deposited and post-annealed films grown from an in-house fabricated target. Annealed films grown from the new commercial target exhibited improved consistency in T -dependent transport and magnetization properties, independent of growth temperature. None of the as-grown sputter deposited films grown in the ArO 2 mixture exhibited a metallic transition while those grown in Ar-only at T s > 800°C had a range of transition temperatures between 110 and 180 K. The variation in substrate-dependent structure demonstrated again the sensitivity of growth mechanism to template. Finally, the 500°C film grown in the ArO 2 mixture, went from insulating at all T 's to exhibiting a 215°C metallic transition after the reducing anneal treatment.

Muon spin rotation (μSR) spectra in the non-Fermi-liquid (NFL) heavy-fermion alloys UCu5−xPdx (x = 1.0 and 1.5) and CeCu5.9Au0.1 yield estimates of the rms width (δχ)rms of the inhomogeneous susceptibility distribution in these systems. In UCu5−xPdx, the temperature dependence of (δχ)rms indicates a wide distribution of Kondo temperatures TK, resulting in a significant number of uncompensated U spins with low TK which cause NFL behavior. In contrast, μSR lines in CeCu5.9Au0.1 are too narrow for such “Kondo disorder” to account for NFL properties unless, as seems unlikely, the correlation length for the susceptibility disorder is long in this alloy.

Although the unconventional character of the superconductivity in pure and doped UBe 13 has been well established, the precise nature of the superconducting order parameter is still unknown. We present muon spin rotation measurements in boron-doped UBe 13 showing a paramagnetic frequency shift below the superconducting transition temperature which is nearly independent of applied magnetic field (0.01-0.10 T), unlike a conventional Knight shift. No increase in line width is observed in zero field. These results are compared to observations of the paramagnetic Meissner effect in other superconductors, and are discussed in terms of the possible alignment of spin or orbital moments associated with unconventional superconductivity in this system.

Magnetic properties of the Li‐doped cuprates La2Cu1-xLixO4 (where x=0.01,\ 0.05,\ 0.10,\ 0.45, and 0.50) have been studied by μSR. For low Li concentrations (x\Eleq 0.10) we find a rapid suppression of TN as x increases, but little change in the magnitude and temperature dependence of the AFM order parameter. This indicates that Li doping effectively destroys AFM (similar to Sr doping, but different from Zn doping) without strongly affecting the onsite Cu moments and the shape of the spinwave excitation spectrum. For high Li concentrations we find magnetic clusters in about 15% of the sample volume; the remaining volume is non‐magnetic, suggesting possible singlet‐state formation.

We present μ+ paramagnetic shift measurements between 12 K and about 65 mK in cerium magnesium nitrate (CMN) to investigate its utility as an in‐situ temperature calibration source for low temperature μSR experiments. CMN is a salt which exhibits Curie‐law susceptibility to temperatures as low as 5 mK. The μ+ Knight shift is measured to be -(1.46\pm 0.03)\times 10-3/T+(0.004\pm 0.02)\times 10-3, corresponding to a transferred hyperfine field of -39 Oe/\mu_ B.