L. V. Elokhina

Acoustic and magnetic properties of La0.825Sr0.175MnO3 lanthanum manganites

This paper reports on measurements of the acoustic, magnetic, and electrical properties and on an x-ray microprobe analysis of a La0.825Sr0.175MnO3 single-crystal sample. The acoustic studies were made with a pulsed acoustic spectrometer operating on a 770-MHz carrier. The studies revealed anomalies in the damping coefficients and sound velocity near 300, 200 K, and the Curie temperature TC (283 K) where the colossal magnetoresistance occurs. The effect of a magnetic field on the magnetic texture of lanthanum manganites cooled below TC, observed earlier in samples of other composition, is confirmed. In addition, a region was found wherein the magnetic susceptibility of an unclamped sample behaves anomalously. The electrical resistivity was observed to decrease substantially below TC; this effect exhibits a hysteretic pattern in the interval 200–180 K.

Phase transformations in CuO caused by bombardment by He+ ions and by the action of spherical shock waves

The valence state of copper ions and the phase composition of copper monoxide CuO subjected to bombardment by He+ ions and explosive shock waves are studied by the methods of x-ray photoelectron spectroscopy (XPS) and x-ray emission spectroscopy (XES). Measurements of photoelectron Cu 2p and emission O Kα spectra revealed a decrease in the concentration of Cu2+ ions and partial reduction of CuO to Cu2O as a result of both ion bombardment and shock-wave loading. The concentration of the Cu2O phase attained values of 10–15%. The Cu2O phase is revealed by the XPS and XES methods even at concentrations lower than its threshold concentration for detection by x-ray diffraction measurements. This points to the effectiveness of XPS and XES techniques in studying nanocrystalline materials and defect structures containing finely dispersed inclusions. A model for the emergence of Cu2O due to the formation of charged clusters under the action of stress waves is proposed.

Elastic and magnetic properties of the La0.6Pr0.1Ca0.3MnO3 single crystal

The temperature dependences of the velocity of longitudinal sound, internal friction, and magnetization of the single crystal with the nominal composition La0.6Pr0.1Ca0.3MnO3 have been measured. It has been found that the substitution of praseodymium for lanthanum in La0.7Ca0.3MnO3 leads to a decrease in the velocity of sound and to an increase in the spontaneous magnetization. The method of determining the Curie temperature distribution function during a first-order transition has been proposed. It has been shown that, in the crystal under study, this function is asymmetric.

Charge state of manganese ions and the nonstoichiometry of Ca1 − xLayMnO3 − δ single crystals

The charge states and effective spins of manganese ions in nonstoichiometric single crystals of Ca1 − xLayMnO3 − δ (x = 0, 0.05, 1) manganites have been determined from the exchange splitting of Mn 3s X-ray photoelectron spectra. The chemical composition of the manganite samples under investigation, including the concentration of oxygen, has been determined using the data of the X-ray microanalysis of cations. It has been found that the manganite single crystals under investigation have large defectiveness in both the cation and oxygen sublattices. The efficiency of the complex use of 3s photoelectron spectroscopy and X-ray microanalysis in the determination of the charge state of manganese ions and violations of stoichiometry in doped and defected manganites has been demonstrated.

X-ray spectra and specific features of the structure of lithium-sodium cobaltite LixNayCoO2

The electronic structure and specific features of the structure of nonstoichiometric cobaltite LixNayCoO2 (x = 0.42, y = 0.36) have been studied comprehensively. The calculated multiplet for the lowspin state of the Co3+ ion agrees with the experimental spectra. It has been established using X-ray absorption spectra measured in the total photoelectric effect yield and total fluorescence yield modes that the LixNayCoO2 cobaltite is stoichiometric with respect to the alkali metal near its surface and is defective inside. It has been demonstrated that the charge compensation in the case of an alkali metal deficit in LixNayCoO2 is due to holes in O 2p states.

Lattice, electrical, and magnetic effects in lanthanum manganites La1−xSrxMnO3 (x = 0.125, 0.150, 0.175)

The temperature dependences of the velocities of transverse and longitudinal hypersound in lanthanum strontium manganites of the composition La1−xSrxMnO3 (x = 0.125, 0.150, 0.175) have been measured at frequencies of 0.5–0.7 GHz. The structural phase transitions have been revealed, and their positions have been confirmed by data on the electrical resistance and magnetic measurements performed using the same samples. The results obtained have been analyzed in the framework of the model of competing Jahn-Teller distortions and magnetic ordering. The anomalies observed in the behavior of the velocities of longitudinal hypersound have been attributed to the local Jahn-Teller distortions, and their suppression due to the magnetic ordering has been considered a possible factor responsible for the colossal magnetoresistance.

Structure and Properties of Ca1-xEuxMnO3 Single Crystals

The crystal growth of electron-doped manganites Ca1-xEuxMnO3 by the floating zone method is reported. The special features of the growth parameters are discussed. Results of x-ray analysis, magnetic and transport characteristics are shown.

Structural, Magnetic and Electrical Properties of the Slightly Doped Lanthanum Manganites

The temperature dependences of the transverse and longitudinal hypersound velocities at the frequencies (0.5-0.7) GHz were measured in the La1-xSrx MnO3 (x = 0.125; 0.15; 0.175) compositions. Structural phase transitions the position of which is confirmed by the electric resistance and magnetic measurements data for the same samples are observed. These results were analyzed within the model of the competing Jahn-Teller distortions and magnetic ordering. Anomalies in the behavior of the longitudinal hypersound velocities were related to the local Jahn-Teller distortions the suppression of which upon magnetic ordering is considered as a possible origin of a colossal magnetoresistance.