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The Fermi National Accelerator Laboratory has measured the anomalous precession frequency $a^{}_\mu = (g^{}_\mu-2)/2$ of the muon to a combined precision of 0.46 parts per million with data collected during its first physics run in 2018. This paper documents the measurement of the magnetic field in the muon storage ring. The magnetic field is monitored by nuclear magnetic resonance systems and calibrated in terms of the equivalent proton spin precession frequency in a spherical water sample at 34.7$^\circ$C. The measured field is weighted by the muon distribution resulting in $\tilde{\omega}'^{}_p$, the denominator in the ratio $\omega^{}_a$/$\tilde{\omega}'^{}_p$ that together with known fundamental constants yields $a^{}_\mu$. The reported uncertainty on $\tilde{\omega}'^{}_p$ for the Run-1 data set is 114 ppb consisting of uncertainty contributions from frequency extraction, calibration, mapping, tracking, and averaging of 56 ppb, and contributions from fast transient fields of 99 ppb., Comment: Added one citation and corrected missing normalization in Eqs (35) and (36)

This paper presents the beam dynamics systematic corrections and their uncertainties for the Run-1 data set of the Fermilab Muon g-2 Experiment. Two corrections to the measured muon precession frequency $\omega_a^m$ are associated with well-known effects owing to the use of electrostatic quadrupole (ESQ) vertical focusing in the storage ring. An average vertically oriented motional magnetic field is felt by relativistic muons passing transversely through the radial electric field components created by the ESQ system. The correction depends on the stored momentum distribution and the tunes of the ring, which has relatively weak vertical focusing. Vertical betatron motions imply that the muons do not orbit the ring in a plane exactly orthogonal to the vertical magnetic field direction. A correction is necessary to account for an average pitch angle associated with their trajectories. A third small correction is necessary because muons that escape the ring during the storage time are slightly biased in initial spin phase compared to the parent distribution. Finally, because two high-voltage resistors in the ESQ network had longer than designed RC time constants, the vertical and horizontal centroids and envelopes of the stored muon beam drifted slightly, but coherently, during each storage ring fill. This led to the discovery of an important phase-acceptance relationship that requires a correction. The sum of the corrections to $\omega_a^m$ is 0.50 $\pm$ 0.09 ppm; the uncertainty is small compared to the 0.43 ppm statistical precision of $\omega_a^m$., Comment: 35 pages, 29 figures. Accepted by Phys. Rev. Accel. Beams

Precise measurement of straw axial coordinate (along the anode wire) with accuracy compatible with straw radial coordinate determination by drift time measurement and increase of straw detector rate capability by using straw cathode readout instead of anode readout are presented., Comment: 16 pages, 10 figures

Detector rate capability is one of the main parameters for designing a new detector for high energy physics due to the permanent rise of the beam luminosity of modern accelerators. One of the widely used detectors for particle track reconstruction is a straw-detector based on drift tubes. The rate capability of such detectors is limited by the parameters of readout electronics. The traditional method of increasing detector rate capability consists in increasing their granularity (the number of “elementary” detectors = readout channels) by reducing the straw diameter and/or by dividing the straw anode wire into two parts (for decreasing the rate per readout channel). A new method of designing straw detectors with a high rate capability is presented and tested. The method is based on dividing the straw cathode into parts and the independent readout of each part.

By means of muon catalysis we study the phenomena in a pt-fusion, which have been previously investigated in the only experiment and now are at the frontier of nuclear few-body physics. The experiment is aimed at measuring the yields of the reaction products: γ-quanta, conversion muons and e + e − pairs. As a result we plan to measure the pt-fusion partial product yields (first time for e + e − pairs) with accuracy not worse than 10%, and this will enable us to obtain the nuclear reaction rates in M1 and E0 transitions in A = 4 system.

A ferrofluid based on Fe3O4 nanoparticles dispersed in heavy water D2O is studied using the μSR method. The experiment has been carried out at temperatures 26–300 K. It is found that the diamagnetic (muon) fraction is formed in the ferrofluid in about the same amount as in D2O, but the muon-spin relaxation rate in the ferrofluid is much higher than in D2O. A significant shift of the muon-spin precession frequency in the ferrofluid is observed. It is shown that the shift of the muon precession frequency as a function of the external magnetic field is described by the Langevin function typical of paramagnetic magnetization. The mean magnetic field in the medium due to magnetic-nanoparticle polarization in an external field is experimentally determined. The nanoparticle sizes are estimated.

The muon spin precession in the axial-symmetric muonium Mubc was studied in a magnetic field applied along the initial muon polarization which was, in turn, parallel to the [111] axis of a silicon single crystal. Hyperfine fields were measured at temperature T = 12 K. The transversal parameter is in good agreement with work by Blazey et al 1983 Phys. Rev. B 27 15, but obtained in this work is less than the value published by Blazey et al by 0.29 MHz. This discrepancy is attributed to the accuracy of determination of the angle between the [111] axis and the magnetic field direction.

We report lSR studies on a Ce 3 Pd 20 Si 6 polycrystalline sample. Zero-"eld measurements were undertaken to gain information on the magnetic ordering at low temperatures. Below 0.4 K the increase of the muon-spin depolarization rate re#ects the development of a quasi-static ordering of magnetic moments of electronic origin probably randomly oriented. In transverse-"eld studies a clear frequency shift was observed. This fact may be ascribed to the increase of the total-magnetic moment of the superparamagnetic cube containing 8 Ce2 atoms and their ferromagnetic ordering with decreasing temperature. ( 2000 Elsevier Science B.V. All rights reserved.

The μSR spectrometer installed on the surface muon beam of the JINR phasotron is described. The possibility of using the surface muon beam with high contamination of positrons in investigations of a solid state by the μSR method is shown. Discrimination of muons from positrons is performed by amplitude analysis and time-of-flight technique. The investigation has been performed at the Laboratory of Nuclear Problems, JINR (Dubna).

The μSR method was used to measure the internal magnetic fields at interstitial sites of the crystal lattice in holmium, where muons are localized. In a simple helicoid structure all interstitial sites are magnetically equivalent, and thus in a μSR experiment only one muon-spin precession frequency should be observed at a given temperature. In the spin-slip structure, the interstitial fields in different sections of the helicoid are different and the frequency spectrum of the muon signal should be more complicated. Most of the ZF μSR measurements were performed on a holmium polycrystal with distinct texture. High-statistics ZF measurements below the Neel temperature were performed also on a holmium single crystal at several temperatures. The experimental spectrum was well described by a single frequency. This fact characterized the magnetic structure of holmium as a simple spiral. At the same time, the high values of the relaxation rate (up to 60 μs −1 at 10 K ), could be due to overlapping of several frequencies.

The lifetimes of a negative muon in the isotopes 132Xe and 40Ar in the solid phase are measured. The lifetime of μ − in the 1s state of the isotope 132Xe is τ(132Xe)=101.7±1.7 ns, which corresponds to a total nuclear capture rate Λc(132Xe)=9.4±0.2 μs−1. The lifetime of μ − in the isotope 40Ar, viz., τ (40Ar)=568±6 ns, corresponding to a capture rate Λc(40Ar)=1.31±0.01 μs−1, is obtained to several times better accuracy as compared to previously published results.

The residual polarization of negative muons has been studied for phosphorus-doped and antimony-doped silicon crystals. The measurements were carried out in a transverse magnetic field of 0.1 T over the temperature region 4 K-300 K. The ionized and neutral states of the pseudo-acceptor were observed in antimony-doped silicon for the first time. The rate of transition from the neutral to the ionized state of the acceptor was found to be equal to over the temperature range 4 K-12 K. The estimated rates of relaxation of the magnetic moment of the acceptor-centre electron shell are and in phosphorus-doped silicon and and in antimony-doped silicon at 4 K and 15 K respectively. The experimental results obtained are interpreted in terms of spin-lattice relaxation of the acceptor magnetic moment and of the acceptor-donor pair formation.

The phase separation (PS) effect in superconducting ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+x} (xl~0.04)$ single crystals with low oxygen mobility was studied via $\ensuremath{\mu}\mathrm{SR}$ spectroscopy, high-resolution neutron diffraction, and magnetic susceptibility. Despite the fact that all crystals are inside the miscibility gap $(0.01lxl0.06),$ only crystals with a sufficiently large excess oxygen concentration $x=0.04$ show a macroscopic phase separation according to the neutron-diffraction data. However, in all samples a phase transition to an ordered magnetic state was observed by $\ensuremath{\mu}\mathrm{SR}$ spectroscopy concomitantly with the onset of superconductivity. This effect is treated as a microscopic phase separation which is possibly driven by superconductivity.

The residual polarization of negative muons in crystal silicon samples with phosphorus (P: 1.6×1013 cm−3) and antimony (Sb: 2×1018 cm−3) impurities is investigated. The measurements are made in a 1000 G magnetic field oriented in a direction transverse to the muon spin in the temperature range 4–300 K. The relaxation rate and shift of the precession frequency in the silicon sample with the phosphorus impurity are measured more accurately than previously. It is found that in antimony-doped silicon the acceptor center µ A1 at temperatures below 30 K can be in both ionized and neutral states. The experimental data are interpreted on the basis of spin-lattice relaxation of the magnetic moment of an acceptor center, formation of acceptor-donor pairs, and recombination of charge carriers at the acceptor. Preliminary measurements showed a nonzero residual polarization of negative muons in germanium.

The compounds Ce 3 Pd 20 X 6 ( X = Ge , Si ) manifest unusual physical properties which would catalogue them as magnetic Kondo systems. Our zero-field μ SR measurements were undertaken to gain information about the magnetic behaviour at low temperatures. The muon spin relaxation rate was found to increase up to value of 4 μ s - 1 at 50 mK. Below 0.3 K an increase in the depolarization rate is believed to represent the development of quasi-static ordering of magnetic moments of electronic origin. A follow-up series of transverse-field μ SR measurements were performed. The external fields were varied up to 5 kOe and the temperature dependence of the internal magnetic field was found to be similar to that found in Ce 3 Pd 20 Si 6 . The μ SR experiments were carried out at the PSI, Villigen, Switzerland.

The dependence of the residual polarization of negative muons in n‐type Si with impurity concentration (1.6\pm 0.2)\times 1013\ cm-3 on temperature in the 10–300 K range has been investigated. Measurements were carried out in external magnetic field of 0.08 T transverse to the muon spin. Muon spin relaxation and frequency shift were observed at temperatures below 30 K. The relaxation rate at 30 K is equal to 0.25\pm 0.08\,μ s-1. The frequency shift at 20 K is equal to 7\times 10-3. Both the relaxation rate and the frequency shift grow with decrease of temperature. Below 30 K the relaxation rate is well described by the dependence \varLambda=bT-q, where q=2.8.

Electron spin‐freezing at Tf=8 K has been detected in superconducting (Tc=12\ K) single crystal La2CuO4+y (y\simeq0.03) by ZF‐μSR. According to diffraction data, the crystal is in Bmab phase without any traces of structural phase separation. TF‐μSR experiment has shown that no Abrikosov flux line lattice is formed below Tc. The data allow us to assume that the magnetic and superconducting regions in the crystal are space separated on the microscopic scales ~ 102 A. The presence of large field induced broadening of the Knight shift distribution k\sigma > 1000 ppm indicates that the crystal contains micro‐regions possessing enhanced magnetic susceptibility.

The possibility of investigating by the muonic method spin-incommensurate helicoidal structures of rare-earth magnets is examined for the example of holmium. It is shown that at temperatures 20 K

ZF, LF and TF μSR measurements have been carried out with a polycrystalline CeRuSi2 sample. ZF data show a sharp increase of the muon relaxation rate below the temperature T=12 K (0.42 μ s-1 at T=4.2 K) justifying the phase transition to the magnetically ordered state. The results of LF measurements at T=4.2 K show that the magnetic fields on the muon Bμ, produced by the cerium magnetic moments, are mainly static – external longitudinal field of 150 Oe practically recovers the muon spin polarization. In the paramagnetic phase the polarization decay has an exponential form at all measured temperatures 20 K < T < K, though LF experiment at T=20 K clearly shows a significant static contribution (\sim 75%). This situation is discussed in frames of double relaxation model. The ferromagnetic type of magnetic ordering was proved by hysteresis behavior of (B–H) observed in TF‐experiment.

The residual polarization of negative muons in n-type silicon with impurity density (1.6±0.2) · 1013 cm−3 is investigated as a function of temperature in the range 10–300 K. The measurements are performed in an external magnetic field of 0.08 T oriented transversely to the spin of the muons. Relaxation of the muon spin and a shift of the precession frequency are observed at temperatures below 30 K. The relaxation rate at 30 K equals 0.25±0.08 μs−1. The shift of the precession frequency at 20 K equals 7 · 10−3. Both the relaxation rate and the shift of the precession frequency increase as the temperature decreases. At temperatures below 30 K the relaxation rate is described well by the relation Λ=bT−q, where q=2.8±0.2.

NQR andμSR investigations of the local magnetic field inα-Bi2O3 were performed. In theNQR experiments onα-Bi2O3 which is usually considered as diamagnetic, the splitting of the spectral lines revealed a local field on the bismuth nuclei. The internal magnetic field obtained byμSR significantly exceeds the dipole field from Bi nuclear magnetic moments. A possible source of the local magnetic fields is partial covalent bonds inα-Bi2O3.

TF and ZFμSR-investigations were performed on high purity CuO powder. By TF measurements a phase transition to the ordered state was observed at 227K. A commensurate-incommensurate phase transition was detected at 213K by ZF measurements. In the commensurate phase we observed the Larmor precession. Four signals were detected below 55K, but by increasing temperature above 190K, precession became having only one component. This fact may be explained by muons tunneling between equivalent sites. In the incommensurate phase the Larmor precession was not detected because of too large damping.

Zero field muon spin rotation and magnetic susceptibility experiments on investigation of magnetic properties of cuprateY2Cu2O5 have been performed in the temperature range 4.2–30 K. Transverse fieldμSR-experiments have been also carried out in order to obtain accurate information about transition temperature and to study the influence of the external magnetic field. Our data show that two magnetic phase transitions occur inY2Cu2O5 with lowering temperature. Upper Neel temperatureTN=13 K is consistent with previous experimental data. We obtained the temperature dependence of the local magnetic field on the muonBμ(T) in the antiferromagnetic phase.Bμ(T) reveals a peculiarity (some change of the slope) near the temperatureTN=7.5 K, which can be interpreted as an additional magnetic phase transition caused by a change in magnetic ordering of the copper subsystem. Applying a small external magnetic field 50 Oe leads to smearing of the peculiarity inBμ(T) dependence.

ZF, LF and TF μSR experiments with antiferromagnetic (AF) ceramical samples La2−xSrxCuO4−y have been performed in the temperature range 10–300 K. Zero field muon spin polarization functions obtained below the Neel temperature clearly show a nonzero initial precession phaseϕ∼-−0.35 rad. We propose an explanation based on existence of the dynamical magnetic fields on the muon.

The dependence of the residual polarization of negative muons in p-type Si on temperature in the 4.2–270 K range has been investigated. Measurements were carried out in external magnetic field of 0.08 T transverse to the muon spin. The impurity concentration in the sample was 2 · 1013 cm−3. Muon spin relaxation was observed at temperatures below 30 K. The relaxation rate atT=30 K is equal to 0.18±0.08μs−1. The relaxation rate grows with the decrease of temperature and at 4.2 K exceeds 30μs−1. The value of the residual polarization at zero timeP(t=0) is constant within the investigated temperature range.

A zero magnetic field muon spin rotation study of α-O2 (antiferromagnetic phase of solid oxygen) in the temperature range 10–24 K is presented. Static magnetic order has been observed below the α-β transition temperature. The temperature dependence of the muon precession frequency exhibits a behavior characteristics of the two-dimensional Heisenberg spin-1 system with anisotropy parameter α ∼ 10−2.

Results on the systematics of the magnetic penetration depth ${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$ in the high-temperature superconductors ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{1\mathrm{\ensuremath{-}}\mathit{z}}$${\mathrm{Y}}_{\mathit{z}}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ (z=0,0.1,0.2,0.3,0.4,0.45) and ${\mathrm{Bi}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pb}}_{\mathit{x}}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ (x=0.15,0.30,0.70) are reported from muon-spin-rotation measurements on polycrystalline samples with known oxygen excess \ensuremath{\delta}. In determining ${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$ various additional sources for inhomogeneous internal field distributions, besides the one arising from the flux-line lattice, have been critically taken into account. The most important one arises from a type of powder broadening due to the anisotropy of the field-cooled magnetization. It is found that ${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$ in the Y-doped compounds correlates in the expected manner with the nominal hole-carrier concentration p (${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}^{\mathrm{\ensuremath{-}}2}$\ensuremath{\propto}p) while the Pb-doped compounds ${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$ is practically independent of p. It is concluded that Pb doping (valence state is +2) does not increase the density of free charge carriers in agreement with results from Hall-effect measurements. No correlation between ${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}^{\mathrm{\ensuremath{-}}2}$ and ${\mathit{T}}_{\mathit{c}}$ in the manner seen in the 1:2:3 family is found in the present case.

Muon precession parameters in liquid oxygen as well as α-, β- and γ-phases of crystalline oxygen have been measured in the temperature range 10–90 K. It was found that the muon polarization P =1 in liquid O 2 , γ-O 2 and β-O 2 . The local field at the muon site has been measured in the antiferromagnetic α-phase of oxygen ( B 0 =1.2 kG). The analysis of the data obtained shows that about 40% of the muons in oxygen form a paramagnetic complex (presumably MuO 2 or O 2 Mu + ) and about 60% of them form a diamagnetic compound.

After conversion of the LNP JINR phasotron new opportunities have been opened for μSR-research. A new round of investigations has begun since 1987. In this paper we present the summary of the results achieved and give some prospects for future investigations.

The zero field μSR-method has been used to study the magnetism in the disordered magnetic alloy Fe82−xNixCr18 near the three-critical, pointx=25. The dynamic and static local field distributions are analyzed. The difference between spin-glass states obtained either from the paramagnetic or after the double transition is discussed.

High temperature superconductors HoBa2Cu3O7−δ (T c ≅93 K), Ho0.5Y0.5Ba2Cu3O7−δ (T c ≅93 K) and ErBa2Cu3O7−δ (T c ≅95 K) were investigated by the zero-field μSR-technique. The muon spin depolarisation rate connected with the fluctuation frequency of rare-earth ion magnetic moments was measured. It was found that the samples with holmium show a fast increase of the muon spin depolarisation rate at temperatures below 20 K, while in ErBa2Cu3O7−δ the depolarisation rate remains low in the whole temperature region studied (4.2 K-270 K). The sharp difference between the behaviours of the muon spin depolarisation rate may be explained by the difference between the ground state of Ho3+ and Er3+ ions in the crystalline field of the lattice.

We present the results of investigations of superconducting niobium and high temperature ceramical superconductor La1.9Sr0.1CuO4 by the μSR technique. The experiments with the niobium sample confirm high reliability of the μSR-technique in determining such characteristics of type II superconductors asTc,Hc1,Hc2, the magnetic field penetration depth λ, and the critical current densityJc. The analysis of the field dependencies of the distribution width and mean value of the magnetic fields on the muon when the samples are magnetized is carried out. A qualitative difference in the behaviour of the magnetic field distribution width in Nb and LaSrCuO is revealed. Whilst the niobium data are well described in the frame of the critical state model, application of a similar approach to the high-Tc superconductor does not give a satisfactory description of our experimental results.

The temperature dependences of parameters of the muon spin relaxation in liquid and crystalline nitrogen have been studied. It has been established that in condensed nitrogen there takes place a fast depolarization of muons. An anomalous behaviour of the amplitude and phase of muon precession is found in the vicinity of the orientation phase transition in solid nitrogen. It has been shown that muon spin relaxation parameters in nitrogen do not change at reduction of the oxygen impurity content from 0.7·10−4 to 10−6. The fast depolarization of muons in condensed nitrogen is apparently due to the formation of muonium atoms. To explain the phenomena observed, a model of the muonium chemical reaction is proposed. The initial phase of the muon precession has been measured as a function of the perpendicular magnetic field to determine the state of short-lived muonium in nitrogen. It has been determined that muonium in nitrogen is in an excited state. Consideration of the nuclear hyperfine interaction of muonium in condensed nitrogen makes it possible to give a qualitative explanation for the temperature dependence of the initial amplitude of the muon precession.

We report the results of μSR investigations of the ceramic samples La2-xSrxCuO4-σ (x=0.1, 0.15, 0.25) and ReBa2Cu3O7-σ (Re=Er, Ho, Y0.5Ho0.5) in the external magnetic field 0–800 Oe. The measurements were performed by the ZFC and FC methods. The irreversibility effects were studied at several temperatures by measuring the mean value and the width of the magnetic field distribution on the muon in the step by step procedure of increasing and subsequent decreasing of the external field. The temperature dependences of the magnetic penetration depth perpendicular to the basal plane λ⊥ were obtained. For the lanthanum sample with 0.15 of Sr its value at the zero temperature is λ⊥ (0)=2400 A, for Er-Ba-Cu-O λ⊥ (0)=1600 A.

T-474 at SLAC is a prototype BPM-based energy spectrometer for the ILC. We describe magnetic measurements and simulations for the 4-magnet chicane used in T-474.

The muon spin relaxation was measured in the high-Tc superconductors Bi2(Sr1.3Ca0.7)CuO6.2, Bi2Sr2CaCu2O8.16, (Bi1.85Pb0.15)Sr2CaCu2O8.18 and (Bi1.83Pb0.25)Sr1.97Ca1.97 Cu3.07Ox. The data were analysed in order to determine the London penetration depth lambda ab parallel to the basal plane. In all investigated samples lambda ab revealed a temperature dependence which can be explained with the framework of conventional BCS theory in the weak coupling limit.

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.

The spin relaxation rate of anomalous muonium in a longitudinal magnetic field was measured in a silicon single crystal. The results are treated as the diffusion of anomalous muonium in a silicon crystal.

The International Linear Collider and other proposed high energy e+ e- machines aim to measure with unprecedented precision Standard Model quantities and new, not yet discovered phenomena. One of the main requirements for achieving this goal is a measurement of the incident beam energy with an uncertainty close to 1e-4. This article presents the analysis of data from a prototype energy spectrometer commissioned in 2006--2007 in SLAC's End Station A beamline. The prototype was a 4-magnet chicane equipped with beam position monitors measuring small changes of the beam orbit through the chicane at different beam energies. A single bunch energy resolution close to 5e-4 was measured, which is satisfactory for most scenarios. We also report on the operational experience with the chicane-based spectrometer and suggest ways of improving its performance., To be submitted to Journal of Instrumentation

The lifetime of negative muons in the 129Xe 1s state was measured. The muon capture rate in 129Xe is compared with that in the 132, 136Xe isotopes. The capture rate was found to depend on the mass number of the cited isotopes. The experimental results are compared with the results of calculations by the semiempirical Goulard-Primakoff formula.

μSR—muon spin rotation—and neutron diffraction measurements have been performed with the superconducting La2CuO4+y having an excess oxygen concentration inside the miscibility gap. The crystals belong to the series of high quality single crystals of La2CuO4, which after being doped with extra oxygen, do not reveal any macroscopic structural phase separation for y≤0.03, verified by X-ray and neutron diffraction. The crystal with y = 0.03 undergoes a transition to a short-range ordered magnetic state of spin-glass type. The crystal with y ⋍ 0.02 becomes antiferromagnetic (AFM) below 15K, according to μSR data. However, neutron diffraction do not reveal long range AFM order, implying that coherent regions of AFM phase are too small to be detected as a Bragg reflection. In addition to magnetic ordering the crystals reveal superconductivity with Tc close to TN,f. Presence of magnetic and superconducting transitions in structurally homogeneous system allows the speculation in terms of microscopic or electronic phase separation providing small hole-rich and hole-poor regions, possessing SC and magnetic order respectively.

μSR investigation of magnetic properties of Y 2 Cu 2 O 5 has been performed in the temperature range 4.2–30 K. Besides the known magnetic phase transition at T N1 = 13 K the peculiarity in the temperature dependence of the local magnetic field on muon was observed near T N2 = 7.5 K. The applying of a small external magnetic field of 50 Oe leads to smearing of this peculiarity.

We have performed the muon spin rotation (SR) measurements of the magnetic penetration depth λ in the superconducting ceramical samples BaPb1−xBixO3 with the bismuth content x=0.22, 0.24, 0.26. The magnetic penetration depth has the low temperature value λ(4.3K) = 7900A for x=0.24. The temperature dependence λ(T)−2 have linear behaviour without any saturation down to the temperature 4.3 K.

Muon spin relaxation and neutron diffraction measurements were performed in Y and Pb substituted Bi-2212 superconductors in order to study the correlation between T c and hole density. We observe first an increase of both T c and the superconducting carrier density via hole transfer, but subsequently (at higher “doping”) more and more holes are prevented from forming superconducting pairs.

The superconducting carrier density n , was measured by means of μ + SR spectroscopy in the mixed phase of a series of polycrystalline Bi-based 2212 superconductors with different substitution of Bi 3+ by Pb 2+ . In exactly the same samples the effective valence per Cu-atom V ( Cu ) was determined by neutron powder diffraction. We observed that n , and V ( Cu ) are not proportional to each other in the heavily doped region. This behavior is interpreted as evidence that the carriers become more and more localized with increasing lead content.