The μSR study of the relaxation of Ho and Er magnetic moments in high-Tc 1-2-3 compounds

High temperature superconductors HoBa₂Cu₃O_7−δ (T _c ≅93 K), Ho_0.5Y_0.5Ba₂Cu₃O_7−δ (T _c ≅93 K) and ErBa₂Cu₃O_7−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 ErBa₂Cu₃O_7−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.     

Comparative asymptotics of solutions and trace formulas for a class of difference equations

Properties of Jacobi operators generated by Markov functions are studied. The main results refer to the case where the support of the corresponding spectral measure µ consists of several intervals of the real line. In this class of operators, a comparative asymptotic formula for two solutions of the corresponding difference equation, polynomials orthogonal with respect to the measure µ and functions of the second kind (Weyl solutions) is found. Asymptotic trace formulas for the coefficients a _n and b _n in this difference equation are obtained. The derivation of the asymptotic formulas is based on standard techniques for studying the asymptotic properties of polynomials orthogonal on several intervals and consists in reducing the asymptotic problem to investigating properties of solutions to the Nuttall singular integral equation.     

High-current electron gun with a field-emission cathode and diamond grid

Control grids used in high-current devices with field emission cathodes should be made of an appropriate, “grid-grade” material. Such a material must offer a high mechanical strength, thermal conductivity, and electric conductivity. In addition, grids as thin as several microns must be available. As a grid material, boron-doped diamond is tested.     

Effect of 4d metal impurities on the structure, electronic properties, and stability of hexagonal WC from data of FLAPW-GGA calculations

This paper reports on the results of systematic ab initio full-potential linearized augmented plane wave (FP-LAPW) calculations of the band structure and a number of properties of hexagonal tungsten carbide h-WC doped by all 4d metals (M = Y, Zr, ..., Ag). The lattice parameters, distributions of the density of states, energies of formation and cohesion, low-temperature heat capacity coefficients, and Pauli paramagnetic susceptibilities of the WC: M systems have been determined for the first time and discussed in comparison with those for h-WC doped by 3d atoms. It has been found that the change in these properties of the WC: M systems as a function of the type of M atom has a nonmonotonic character.     

Dependence of Poiseuille slip and thermal creep on the law of interaction of gas molecules with the boundary surface

The problem of gas slip at a plane wall is solved on the basis of a linearized kinetic equation with a model collisional term (the S-model, which provides the correct value of the Prandtl number). Expressions are obtained for the Poiseuille slip and thermal creep which contain integrals of the scattering kernel over the velocity half-space. These expressions are made concrete for three particular cases corresponding to well-known models of the scattering kernel.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 107–114, November–December. 1977.     

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±0.08s^–1. The relaxation rate grows with the decrease of temperature and at 4.2 K exceeds 30s^–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 =B·T^–q, whereq=2.75. Power dependence of may evidence the essential role of the phonon mechanism in the relaxation of the electron momentum of the acceptor center.The authors express their gratitude to V.B. Brudanin and I.A. Yutlandov for providing the sample, and to Yu.B. Gurov for advices.     

The MSR-investigation of antiferromagnetic phase transitions in erbium

The muon spin relaxation rate (T) in an orientated polycrystalline sample of erbium constructed of large monocrystals has been measured for temperatures 20 <T<300 K. It has been shown that the (T) for erbium is bounded from above asT T_N, whereT _N=84.4 K is the Néel temperature. This fact may be explained by assuming that atT=T_N erbium undergoes a weak phase-transition of the first order.