Magnetic, resonance and transport properties of nanopowder of La0.7Sr0.3MnO3 manganites

X-ray powder diffraction, magnetization, transport and magnetic resonance measurements of nanosize La_0.7Sr_0.3MnO₃ (LCMO) manganites have been performed. The nanosize manganites were synthesized with a co-precipitation method at different (600, 700, 800 and 1000 °C) temperatures. The crystal structure of the nanopowders obtained was determined to be perovskite-like with a rhombohedral distortion (the space group R3¯c). The average size of synthesized nanoparticles (from 17 to 88 nm) was estimated using the X-ray diffraction and low temperature adsorption of argon methods. All the nanosize manganites show ferromagnetic-like ordering. Both the Curie temperature and magnetization decrease with reducing the particle size. The decrease of magnetization is due to the disordered surface shell of particles. The disordered surface layer is a source of the surface anisotropy and is responsible for the increase of coercivity. Temperature dependences of the magnetic resonance spectra parameters have allowed obtaining information on dynamics of magnetic properties in the nanoparticle systems. The resistivity was established to become higher by reducing the particles’ size and increases to a great extent in nanoparticles with the smallest average size at low temperatures. The magnetic entropy was shown to be smaller for the small particles. Using the temperature dependence of magnetic entropy the relative cooling power of the nanosize samples studied was evaluated.     

Effect of coalescence and of the character of the initial oxide on the photoluminescence of ion-synthesized Si nanocrystals in SiO<Subscript>2</Subscript>

The photoluminescence intensity (PLI) related to Si nanocrystals in a SiO₂: nc-Si system synthesized by ion implantation is studied experimentally and theoretically as a function of the Si+ ion dose at various annealing temperatures T_ann (1000–1200°C). The dose corresponding to the maximum PLI is found to decrease with increasing T_ann. These data are explained in terms of a model taking into account the coalescence of neighboring nanocrystals and the dependence of the probability of radiative recombination of quantum dots on their size. It is found that, when silicon oxide is grown in a wet atmosphere, the photoluminescence spectrum contains an additional band (near 850 nm), which is related to shells around the nanocrystals. This band weakens abrupily after high-temperature annealing in an oxidizing atmosphere (air).     

Correcting the Magnetic Field of the Nuclotron Booster

Physics of Particles and Nuclei Letters - The nonlinear dynamics of the 197Au31+ ion beam in the booster has been studied with the MAD-X program. The numerical computation of the dynamic aperture...     

Polarized deuterons and protons at NICA@JINR

The novel scheme of proton and deuteron polarization control in the NICA collider at Dubna is proposed. By means of two Siberian Shakes with solenoid magnetic field the beam spin tune is shifted to the “zero” spin resonance vicinity, whereas manipulation of the polarization is realized by “weak” field solenoids. The scheme makes it possible to obtain any desired direction of the polarization in the both MPD and SPD detectors for any sort of the particles. The possibility of the beam polarization control in the orbit plane at any azimuth of the collider magnetic arcs exists also. The last gives necessary flexibility of optimal matching the beam polarization at injection into collider and at the polarimetery monitor points.     

Synthesis of 6-Alkoxy- and 1,6-Dialkoxy-4-amino-1-aryl-3-oxo-2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-7-carbonitriles

Russian Journal of Organic Chemistry - Base-catalyzed reaction of 3-aroyl-6-halopyridine-3,5-dicarbonitriles with alcohols involved successive regioselective pyrrole ring fusion at the pyridine [c]...