Study of the heavy-fermion compound CeRu<Subscript>2</Subscript>Si<Subscript>2</Subscript> by the small-angle neutron scattering method

In order to directly observe neutron scattering by heavy fermion quasiparticles at low temperatures, a CeRu₂Si₂ single crystal has been studied by the small-angle neutron scattering method. In the experiment, neutron scattering is observed at T = 0.85 K for momentum transfers q ≤ 0.04 Å^?1, which is treated as the orbital component of magnetic scattering by heavy fermion quasiparticles. It has been found that the application of a magnetic field H = 1 T leads to both an increase in the observed scattering and its anisotropy with respect to the field direction. Moreover, measurements in the magnetic field reveal additional scattering for q > 0.04 Å^?1, which is well described by a Lorentzian and is interpreted as neutron magnetic scattering by spin-density fluctuations with a correlation radius R_c ≈ 30 Å.     

Holomorphic functional calculus for operators on a locally convex space

One-variable holomorphic functional calculus is studied on the bornological algebra Lec(E) of all continuous linear oprators on a complete locally convex space E. It is proven that the following three basic notions of the theory are equivalent: (i) existence of projective resolvent of an operator T at a point λ₀, (ii) strict regularity of λ₀ for the operator T in the sense of [12, 13, 15], (iii) tamability of the operator (λ₀ ? T)^?1 (T if λ₀ = ∞), which means that there is a new equivalent system of seminorms on E, such that the operator is bounded in each of them.     

Renormalization group in the theory of two-dimensional turbulence: Instability of the fixed point with respect to weak anisotropy

A statistical model of fully developed turbulence in two-dimensional space is considered by means of the renormalization group method in the weak anisotropy approximation. It is shown that the corresponding fixed point of the renormalization group equations is not infrared stable. Hence, the weak, anisotropy approximation is not valid for describing two-dimensional turbulence. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 112, No. 3, pp. 417–427, September, 1997.     

Nonlinear properties and paramagnet-to-ferromagnet transition in Nd<Subscript>0.7</Subscript>Ba<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> single crystal with metallic ground state

We present the results from studying the magnetic properties (linear and nonlinear susceptibilities and the depolarization of polarized neutrons) of Nd_{1 − x} Ba _x MnO₃ manganite, x = 0.3, with Curie temperature T _C ≈ 140 K and dielectric-to-metal transition temperature T _DM ≈ 129 K. Its critical behavior corresponds to that of an isotropic 3-D ferromagnet at temperatures above T*≈ 144 K, but a strong nonlinear response in weak magnetic fields and depolarization are observed at temperatures below T*. It is shown that this nontraditional behavior is related to the generation of ferromagnetic clusters in the paramagnetic matrix that form a conducting percolative network at temperatures near T _DM.     

Mesoscopic magnetic inhomogeneities in the low-temperature phase and structure of Sm1−x SrxMnO3 (x < 0.5) perovskite

Results are presented of studies of the ¹⁵⁴Sm_1?x Sr_xMnO₃ system using neutron powder diffraction and small-angle polarized neutron scattering. An analysis of the neutron diffraction spectra showed that at T < 180 K these exhibit typical Jahn-Teller distortions of the manganese-oxygen octahedrons which persist under further cooling and on transition of the sample to a metallic magnetically ordered state. The magnetic contribution to the diffraction is satisfactorily described using the (A _x (A _y )F _z ) model and is interpreted as the coexistence of ferromagnetic and antiferromagnetic phases. The exaggerated widths of the diffraction lines indicate an appreciable contribution from microdeformations evidently associated with the inhomogeneity of the system. Small-angle polarized neutron scattering showed that the Sm system for x = 0.4 and 0.25 is magnetically inhomogeneous in the low-temperature phase. Ferromagnetic correlations occur on scales of around 200 Å and having dimensions greater than 1000 Å which, combined with the temperature hysteresis of the magnetic small-angle scattering intensity observed for an x = 0.4 sample in the low-temperature phase, suggests that the transition is of a percolation nature.     

Comparative study of heterogeneous magnetic state above TC in La0.82Sr0.18CoO3 cobaltite and La0.83Sr0.17MnO3 manganite

The magnetic, transport and structural properties are studied for La_0.83Sr_0.17MnO₃ and La_0.82Sr_0.18CoO₃ single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т^?>T_C in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator–metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn³⁺ and Co³⁺ ions.     

Reduction of Ruthenium(IV) to Ruthenium(III) in Aqueous Alcohol Solutions of Hydrochloric Acid under Microwave Radiation

The behavior of a kinetically inert form of ruthenium(IV), the -oxo-bis-[pentachlororuthenate(IV)] ion [Ru₂OCl₁₀]^4–, was studied in aqueous alcohol solutions of hydrochloric acid under microwave radiation and upon the heating of the solutions. The conditions were selected for the quantitative reduction of ruthenium(IV) to ruthenium(III) with alcohols in 0.6–10 M HCl solutions in a microwave field. The maximum time it takes to reduce ruthenium(IV) under microwave radiation (30 min) was an order of magnitude shorter than that for heating the solutions in a boiling water bath. Regardless of the type of alcohol, the most rapid reduction of ruthenium(IV) was observed at the boundaries of the studied range of hydrochloric acid concentrations. It was found that, under microwave radiation, thermal effects were the driving force of the process in a 0.6 M HCl solution at 98°C, whereas, in 8–10 M HCl solutions, the contributions of nonthermal and thermal effects were comparable. It was shown that the reducing ability of saturated monoatomic C₁–C₄ alcohols increases with the number of carbon atoms and is also due to specific features of microwave radiation.     

Regularities in the Sorption Recovery of Osmium in Various Oxidation States (VIII, VI, and IV) on Silica Chemically Modified with Thiourea Derivatives

Regularities in the sorption recovery of osmium(VIII, VI, IV) on silica chemically modified with thiourea derivatives (N-allyl-N"-propylthiourea (ATUS), N-phenyl-N"-propylthiourea (PTUS), and N-benzoyl-N"-propylthiourea (BTUS)) were studied. The equilibrium attainment time for the solid-phase extraction of osmium(VIII) is 15, 30, and 40 min for ATUS, PTUS, and BTUS, respectively. For the solid-phase extraction of osmium(VI), equilibrium attainment time is independent of the type of the sorbent and is no more than 5 min. The recovery of osmium(IV) at 95°C and equilibration time 120 min is no higher than 5%. The quantitative recovery of osmium(IV) with silica chemically modified with thiourea derivatives is attained on long-term heating and in the presence of tin(II) chloride. Based on the regularities in the sorption recovery of osmium in different oxidation states and its interaction with thiourea in aqueous solutions with low mole ratios, it was suggested that osmium(VIII, VI) and osmium(IV) interact with thiourea and its derivatives including those covalently bonded to the silica surface via different mechanisms.     

Spin correlations and a mesoscopic structure in Ni-Mn-Ga

The mesoscopic structures of the Heusler alloys Ni_49.1Mn_29.4Ga_21.5 and Ni₂MnGa are studied by small-angle polarized neutron scattering in the temperature range 15 < T < 400 K. The characteristic temperatures of phase transformations (ferromagnetic, martensitic, and premartensitic transformations) and the characteristic sizes of mesoscopic inhomogeneities in them have been determined. Differences in the spin dynamics of these phases and magnetic-nuclear interference upon neutron scattering have been revealed. The evolutions of the mesoscopic structures in the nonstoichiometric and stoichiometric alloys are found to be substantially different.