V. A. Zhukov

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.

Study of condensed nitrogen by μSR method

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.

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.

Magnetism in disordered magnetic Fe82−xNixCr18

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.

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.

Relaxation and shift of the precession frequency of the spin of a negative muon in n-type silicon

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.

The Effect of Uniaxial Static Pressure on the Behavior of an Aluminum Acceptor Impurity in Silicon

The effect of uniaxial compression on the behavior of shallow aluminum acceptor centers in silicon has been studied. The μAl impurity atoms were created by implanting negative muons into silicon single crystals doped with phosphorus to 1.6×1013 cm−3 (sample 1) and 1.9×1013 cm−3 (sample 2). The muon polarization was studied in the temperature range 10–300 K. Measurements were performed in a magnetic field of 2.5 kG oriented perpendicularly to the muon spin. The samples were oriented so that the selected crystal axis ([111] and [100] in samples 1 and 2, respectively), the magnetic field, and the initial muon-spin polarization were mutually perpendicular. External pressure applied to the sample along the indicated crystal axis changed both the absolute value of the acceptor magnetic-moment relaxation rate and the character of its temperature dependence.

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.