The magnetically ordered and paramagnetic states of erbium at temperatures T < T, and T > TN, where TN = 84.4 K is the NCel temperature, have been studied by the muon method. A large crystalline specimen of erbium was used with preferred orientation of the hexagonal c axes of the individual single crystals. The correlation functions GII (T ) and G, ( T ) which describe the fluctuations of the longitudinal and transverse (relative to the c axis) components of the internal magnetic field acting on a muon at T > TN were measured. The G, ( T ) dependence was also measured at T < T,. It is shown that for T > TN the correlator G, is constant over the whole temperature range investigated, TN < T 5 300K, while GII increases to a limited extent as T+TN. The limited range of the GII (T ) dependence as T+TN is regarded as an indication that a weak first-order phase transition takes place in erbium at T, = 84.4 K.

NQR and #SR investigations of the local magnetic field in c~-Bi2Oa were performed. In the NQ.R experinaents on a-Bi203 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 by pSR significantly exceeds the dipole field from Bi nuclear magnetic nmments. A possible source of the local magnetic fields is partial covalent bonds in c~-Bi,,O3.

The paper reports on a theoretical calculation of the magnon and phonon contributions to heat capacity of the multisublattice antiferromagnets La2CuO4 and CuCl2.2H2O, the former being the basic compound of a high-T(c) superconductor. It has been shown that it is only in the former that the contribution of exchange magnons to heat capacity at low temperatures is comparable with that of acoustic magnons which results from the quasi-two-dimensionality of its magnetic subsystem. Heat capacity of La2CuO4 was measured in the range 4.5-25 K, and specific features associated with the magnon contribution were revealed.

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.

NQR and muSR investigations of the local magnetic field in alpha-Bi2O3 were performed. In the NQR experiments on alpha-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 by muSR significantly exceeds the dipole field from Bi nuclear magnetic moments. A possible source of the local magnetic fields is partial covalent bonds in alpha-Bi2O3.

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.

Positive muons have been used to study the local magnetic fields in the oxide alpha-Bi2O3 employed in the manufacture of high-temperature bismuth superconductors. The measured internal magnetic field substantially exceeds the dipole magnetic fields due to the magnetic moments of Bi, but is smaller than the magnetic fields characteristic of paramagnets. The local magnetic fields may be due to a partially covalent bonds in alpha-Bi2O3.

The rate of relaxation of the muon spin (muSR) has been measured in single-crystal nonoriented grains of YBaCu3O6.89 and in the ceramics EuBa2Cu3O6.84 to determine the penetration depth lambda of the magnetic field. The measurements have been carried out under cooling in a magnetic field of 2.5 kG in the temperature range 10 < T < 100 K. The experimental value of the mean-square deviation of the frequencies of the muon precession [DELTAomega2]1/2(T --> 0) is congruent-to 2.5 musec-1, which corresponds to a depth of penetration of the field perpendicular to the CuO2 planes lambda(ab) (0) congruent-to 1600 angstrom. The resulting value of the mean-square deviation of the frequencies is significantly smaller than the values of [DELTAomega2]1/2 is-proportional-to 1/lambda2 corresponding to the penetration depth lambda(ab) (0) = 1300-1400 angstrom obtained in most studies of the muSR. The low value of [DELTAomega2]1/2 may be due to pinning of ''vortex spots''' in superconducting planes of CuO2. The result obtained in the present study casts doubt on the validity of the traditional view of the penetration depth lambda(muSR) measured in a muSR experiment as a lower limit on lambda (lambda greater-than-or-equal-to lambda(muSR)) in highly anisotropic high-temperature superconductors.

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.

Памяти Аркадия Бенедиктовича Мигдала, Беляев С.Т., Вакс В.Г., Гуревич И.И., Коган В.И., Ларкин А.И., Окунь Л.Б., Понтекорво Б.М., Саперштейн Э.Е., Скринский А.Н., Суетин В.А., Трубников Б.А., Халатников И.М., Ходель В.А.

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.

The magnetic field at the muon site in the antiferromagnetic state of samarium at T = 16-105 K is measured. A muon is shown to be localized at the octahedral intersite of a crystal. Due to antiferromagnetic ordering at T2 = 14 K in the zero external magnetic field the temperature behavior of the magnetic susceptibility is measured. The corresponding paramagnetic temperature THETA = -6.7 K is found. The local magnetic field of polarized conductive electrons at the muon site is measured as well.

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.