V. Vassiliev

Penetration of the electromagnetic waves through doped lanthanum manganites

Penetration of the electromagnetic field through plate-shaped bulk polycrystalline sintered Pb and Y–Ba doped manganite samples is studied in the frequency range from 20 kHz to 30 MHz. Strong magnetic-field dependence of the transmission coefficient is observed. The penetration data are compared with the other magnetic-field dependent parameters: the magnetic permeability, magnetoresistance, and magnetoimpedance. Unusual frequency dependence of the penetration depth is observed.

The effect of annealing on the magnetoresistance of polycrystalline (La - Y - Ca) perovskites

The magnetization, resistivity and magnetoresistance of yttrium-doped polycrystalline have been studied as a function of annealing conditions. The magnetoresistance amplitude depends upon the annealing time, with an optimum corresponding to 12 h annealing at under oxygen. Different contributions to the magnetoresistance are separated; the first is related to the technical magnetization, the second, dominant one, to the influence of the total magnetic induction on the band splitting and the spin correlation function.

Semiconductor-metal transition and magnetoresistance in (La,Ca)MnO3 : Experiments and simple model

The effect of Ca-doping on bulk samples of La1−xCaxMnO3 has been investigated, as well as the effect of sample annealing under air and oxygen. The maximum magnetoresistance is observed for ferromagnetic samples, with La0.67Ca0.33MnO3 composition, annealed at an optimum temperature of 1200°C. A simple phenomenological model has been used which describes the magnetic and transport properties as resulting from an exchange-induced band-crossing SC-metal transition.

Charge carriers in La0.67−xYxBa0.33MnO3

Magnetic, magnetotransport and optical properties are experimentally studied. The mechanism of conduction is found to be different below and above the Curie temperature. This difference is explained by a shift of the mobility edge due to magnetic disorder.

Influence of annealing conditions on the magnetoresistance of (LaYCa) manganites

Abstract The resistivity, magnetization and magnetoresistance of (La, Ca) and yttrium-substituted manganites La0.67−xYxCa0.33MnQ3 have been studied as a function of annealing conditions under air or oxygen. Doping by Y decreases the Curie temperature and drastically increases the zero field resistivity peak value. For yttrium doped manganite, annealing at 1400°C for 1 h leads to an increase of the maximum value of magnetoresistance up to 94.6% in applied field of 5 T at 150 K and drastically improves the field sensitivity in small fields (70% in 1 T). Conversely, the MR at room temperature is highest for the undoped sample annealed at 1200°C under oxygen.

A MAGNETIC PAIR-BREAKING EFFECT IN RARE EARTH-DOPED MANGANITES

The magnetic properties of La0.60R0.07Di0.33MnO3 ferromagnetic manganites (Di = Sr, Ba) are studied, where La is partly replaced by magnetic rare earths R. It is shown that (i) there is a ferromagnetic coupling between Mn and R spins, (ii) the Curie temperature is lowered compared to the parent La compound and (iii) its depression is correlated with the effective moment of the rare earth ion. This last relation is tentatively explained by a magnetic pair-breaking effect, where fluctuating R moments lower the double-exchange coupling between Mn atoms.

Chemistry of interactions in the La2O3-MO(MCO3)-Mn2O3, M = Ca, Sr, Ba, Cd systems

Abstract The sequence of phase transitions in the system La 2 O 3 -MO(MCO 3 )Mn 2 O 3 , (M=Ca, Sr, Ba, Cd) and the span range of La 1−x M x MnO 3±δ solid solutions formed were studied. It is demonstrated that interaction begins at 650°C due to formation of divalent metal manganites. Just simultaneously as a result of oxidation-reduction processes and structural transformations the synthesis of small quantities of solid solutions takes place, which is kinetically favoured in the case of smaller divalent metal cations. The chemical transformation finishes at 1200°C. The values of x at all systems are near 0,35. The absence of CdMnO 3 composition in the system CdO-MnO is proved.

Stochastic oscillations of magnetic flux in the toroid sample of lead-doped lanthanum manganite

The dynamics of magnetic flux variations in a toroidal sample of the La0.6Pb0.4MnO3 manganite was investigated. Experiments were carried out when the ac magnetic field was applied perpendicular to the dc one. It is shown that under some conditions, several regimes of complex oscillations of magnetic flux can be excited. Evolution of these oscillations as a function of frequency of ac and magnitude of dc magnetic fields was investigated. The signs of existence of the stochastic regime of oscillations were found.

Galvanomagnetic effects in La2/3D1/3MnO3(D = Ba, Sr) near metal- insulator transition point

The magnetoresistance and Hall effect data for polycrystalline samples of La 2/3 D 1/3 MnO 3 (D = Ba, Sr) have been analyzed. It has been revealed that the peculiarities of galvanomagnetic properties take place at the metal-insulator transition temperature which is less than the Curie temperature. The anomalous Hall coefficient is almost three orders of magnitude larger than the normal Hall coefficient. The effects observed have been explained by the shift of the mobility edge.

Phase diagram for the system Bi2O3CaOSrOCuO in the SrO-rich region

Abstract It has been found experimentally that phase diagram for the system Bi 2 O 3 CaOSrOCuO in SrO-rich region at 850°C in the open air includes three elementary tetrahedra: CaOSrOSr 6 Bi 2 O 11 Sr 2 CuO 3 , CaOSr 2 CuO 3 Sr 6 Bi 2 O 11 Sr 3,5 Ca 0,5 Bi 2 O 7 and Sr 3 Bi 2 O 6 Sr 6 Bi 2 O 11 Sr 3,5 Ca 0,5 Bi 2 O 7  Sr 2 CuO 3 . In the considered interval of corresponding oxide concentrations quaternary oxides are not formed under the above conditions.