V. G. Olshevsky

Investigation of the behaviour of the impurity atoms in Si by μ−SR-method

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.In the rangeT<30 K data on the relaxation rate are well described by the dependence λ=B·T−q, whereq=2.75. Power dependence of Λ may evidence the essential role of the phonon mechanism in the relaxation of the electron momentum of the acceptor center.

ANOMALOUS FREQUENCY SHIFT OF NEGATIVE MUON SPIN PRECESSION IN N-TYPE SILICON

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.An analysis of present and earlier published data on behavior of negative muon polarization in silicon is given. A possible mechanism of relaxation and frequency shift of muon spin precession in silicon is considered.

On the nature of the muon complex in condensed oxygen

Abstract 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.

Weird muonium diffusion in solid xenon

Abstract Muon and muonium spin rotation and relaxation parameters were studied in liquid and solid xenon. The small diamagnetic fraction (∼10%) observed in condensed xenon is believed to be Xeμ + . The muonium hyperfine frequency was measured for the first time in liquid Xe and was found to be in agreement with the vacuum value. A nonmonotonic temperature dependence of the muonium relaxation rate probably indicates that muonium diffusion in solid Xe is of quantum nature.

Study of local magnetic fields in the oxide α-Bi2O3 byNQR andμSR techniques

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.

μSR investigation of cupric oxide

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.

The μSR investigations on the phasotron at Dubna: The present and the future

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.

μSR study of intermediate heavy fermion system CeRuSi2

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.

Antiferromagnetic solid oxygen studied by positive muons

We present a zero magnetic field muon spin rotation study ofα-O2 (antiferromagnetic phase of solid oxygen) in the temperature range of 10–24 K. Static magnetic order has been observed below theα-β transition temperatureBαβ=23.8 K. The temperature dependence of the muon precession frequency exhibits behavior characteristic of a two-dimensional Heisenberg spin-1 system with the anisotropy parameterα ∼ 10−2 quite similar to that of antiferromagnetic phase of the high-temperature superconductor parent compounds. A unique local field at the muon site has been determined to beB0=1.27(5) kG at low temperatures.

The comparative study of irreversibility effects in Nb foil and high-temperature superconducting ceramics by μSR

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.