V.Yu. Pomjakushin

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.

Neutron diffraction study of phase separation in La2CuO4+δ single crystals

Abstract Single crystals of La 2 CuO 4+δ with δ = 0.03 and δ = 0.04 have been studied in the temperature region 10 K ≤ T ≤ 293 K using a high resolution neutron diffractometer. In both crystals, the concentration of excess oxygen is inside the miscibility gap. However, the La 2 CuO 4.03 crystal does not undergo a phase separation — homogeneous oxygen distribution was preserved over the entire temperature region studied, while in the La 2 CuO 4.04 crystal, the phase separation phenomenon, connected with excess oxygen diffusion was observed. Analysis of the diffraction peak width as a function of interplane spacing allowed us to determine the dimensions of the coherent regions of coexisting phases: 975 ± 22 A in the direction of the tetragonal axis of the high temperature phase, and (1460 ± 160) A in the perpendicular direction. Our data provide direct evidence that both the oxygen-rich and oxygen-poor regions have the same Cmca space symmetry.

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 (1.6pm 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 0.25pm 0.08,μ s-1. The frequency shift at 20 K is equal to 7times 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.

Spin-glass ordering in non phase separated La2CuO4.03 studied by μSR

Abstract Electron spin-freezing at Tf = 8 K has been detected by muon spin rotation μSR in a superconducting (Tc = 12 K) single crystal of La2CuO4+y ( y ⋍ 0.03) . The sample belongs the series of La2CuO4 single crystals, 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. At T = 2.5 K the crystal fraction with frozen electronic moments amounts to more than 65% of the crystal volume. The shape and parameters of the muon spin polarization function are typical for the Cu2+spin-glass-like state.

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.

Structure of non-phase-separated La2CuO4.03 studied by single-crystal neutron diffraction

Abstract The structure of a La 2 CuO 4+ y single crystal with the excess oxygen content y =0.03 has been studied by means of neutron diffraction at T =13 K. Although the extra oxygen content of y =0.03 is inside the miscibility gap of La 2 CuO 4+ y (0.01 y Cmca symmetry. It was confirmed that the extra oxygen, O4, is located close to the site (1/4, 1/4, 1/4). The structural parameters for all atoms lay between those previously determined for the oxygen-poor and oxygen-rich phases representing the edges of the miscibility gap, y =0.01 and 0.06, respectively. Our data allow us to conclude that (1) the phase-separated and non-phase-separated La 2 CuO 4+ y compounds are structurally identical, and (2) the crystal structure of La 2 CuO 4+ y changes monotonically when the extra oxygen content changes from 0 to 0.05.

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.

On a generalization of the Kubo-Toyabe formula

Abstract We have derived an analytical form of the muon depolarization function Gz(t) when the magnetic field on the muon can be treated as a sum of two fields with Gaussian and δ-function distributions. We discuss the application of our results to processing μSR data on Laue5f8Srue5f8Cuue5f8O polycrystal samples.

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.