V. N. Duginov

Shallow acceptor centres in silicon studied by means of spin rotation of negative muons

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.

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.

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.

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.

Investigation of acceptor centers in semiconductors with the diamond crystal structure by the μ− SR method

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 µA1 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.