I. E. Korsakov

Volatile Surfactant‐Assisted MOCVD: Application to LaAlO3 Thin‐Film Growth

A new approach to the CVD of oxides with kinetically hindered diffusion, called volatile surfactant-assisted (VSA) metal-organic chemical vapor deposition (MOCVD), consisting of film deposition in the presence of a volatile low melting point oxide (Bi 2 O 3 ) has been developed. The process was applied to the deposition of LaAlO 3 films, and a model of the process was proposed. Epitaxial and textured LaAlO 3 films on various substrates were obtained, both by thermal and VSA MOCVD. A marked improvement in crystalline quality and surface morphology was found for the films deposited by VSA MOCVD. LaAlO 3 films obtained in the presence of Bi 2 O 3 did not contain Bi. A significant increase (up to five times) of the deposition rate was observed for LaAlO 3 films deposited by VSA MOCVD compared with that for the films grown by thermal MOCVD.

Structure and magnetocaloric properties of La1-xKxMnO3 manganites

Abstract A technology of obtaining the single-phase ceramic samples of La1−xKxMnO3 manganites and the dependence of their structural parameters on the content of potassium has been described. Magnetocaloric effect (MCE) in the obtained samples has been measured by two independent methods: classical direct methodic and a method of magnetic field modulation. The values of MCE obtained by both methods substantially differ. The explanation of the observed divergences is given. The correlation between the level of doping and MCE value has been defined. The value of TC determined by the MCE maximum conforms with the literature data obtained by other methods.

Magnetocaloric properties of La1-xKxMnO3 manganites

A technology for obtaining single-phase ceramic samples of La1 − xKxMnO3 manganites, as well as the dependence of their structure parameters on the potassium content, is described. The magnetocaloric effect in the samples has been measured by two direct methods, the classical method and the magnetic field modulation method, and has been calculated from the specific heat data. The values of the magnetocaloric effect obtained by these methods are significantly different. The observed discrepancies have been explained. Correlation between the doping level and the value of the effect has been found. It has been shown that the magnetic-field dependence of variation of the magnetic entropy near TC in weak fields corresponds to theoretical calculations and that the value of the magnetocaloric effect in high magnetic fields can be predicted using this dependence.

Magnetocaloric properties of La{sub 1-x}KxMnO{sub 3} manganites

A technology for obtaining single-phase ceramic samples of La1 − xKxMnO3 manganites, as well as the dependence of their structure parameters on the potassium content, is described. The magnetocaloric effect in the samples has been measured by two direct methods, the classical method and the magnetic field modulation method, and has been calculated from the specific heat data. The values of the magnetocaloric effect obtained by these methods are significantly different. The observed discrepancies have been explained. Correlation between the doping level and the value of the effect has been found. It has been shown that the magnetic-field dependence of variation of the magnetic entropy near TC in weak fields corresponds to theoretical calculations and that the value of the magnetocaloric effect in high magnetic fields can be predicted using this dependence.

Giant magnetorefractive effect in La0.7Ca0.3MnO3 films

Complex experimental investigations of the structural, optical, and magneto-optical properties (magnetotransmission, magnetoreflection, and transversal Kerr effect, as well as the magnetoresistance, of La0.7Ca0.3MnO3 epitaxial films indicate that magnetoreflection and magnetotransmission in manganite films can reach giant values and depend strongly on the magnetic and charge homogeneity of the films, their thickness, and spectral range under investigation. It has been shown that the optical enhancement of the magnetorefractive effect occurs in thin films as compared to manganite crystals. In the region of the minimum of the reflectance near the first phonon band, the resonance-like magnetorefractive effect has been observed, which is accompanied by change of the sign of the magnetoreflection. A model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain this behavior.

Giant magnetorefractive effect in La{sub 0.7}Ca{sub 0.3}MnO{sub 3} films

Complex experimental investigations of the structural, optical, and magneto-optical properties (magnetotransmission, magnetoreflection, and transversal Kerr effect, as well as the magnetoresistance, of La0.7Ca0.3MnO3 epitaxial films indicate that magnetoreflection and magnetotransmission in manganite films can reach giant values and depend strongly on the magnetic and charge homogeneity of the films, their thickness, and spectral range under investigation. It has been shown that the optical enhancement of the magnetorefractive effect occurs in thin films as compared to manganite crystals. In the region of the minimum of the reflectance near the first phonon band, the resonance-like magnetorefractive effect has been observed, which is accompanied by change of the sign of the magnetoreflection. A model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain this behavior.

Heteroligand Lanthanide Dialkyldithiocarbamate Complexes with 1,10-Phenanthroline: A New Approach to Synthesis and Application for the Preparation of Sulfides

A new simple method of synthesis of heteroligand complexes [Ln(Dalkdtc)3Phen] (Ln = Eu or Er; Dalkdtc is the dialkyldithiocarbamate ion, Phen is o-phenanthroline) in an aqueous solution is described; the possibility of using the complexes as initial reagents for the synthesis of rare-earth sulfides is shown.

Heat capacity and magnetocaloric properties of La1-xKxMnO3 manganites

The magnetocaloric effect and the heat capacity of La1 − xKxMnO3 (x = 0.1, 0.15, 0.175) ceramic samples have been studied at temperatures in the range 77–350 K and in magnetic fields of up to 27 kOe. The technique for preparing the samples has been described. The heat capacity anomalies related to the ferromagnetic-paramagnetic magnetic phase transition have been revealed and interpreted. It has been demonstrated that the change in the magnetic entropy ΔS calculated from the data on the heat capacity Cp and direct measurements of the magnetocaloric effect ΔT reaches values that are of practical interest.

Ferroelectric properties in KNbO3 thin films probed by optical second harmonic generation

Ferroelectric phase transitions and the structure of KNbO3 nanometer-thick films deposited by Metal-organic chemical-vapor deposition technique on a MgO(100) substrate are studied. Thin KNbO3 films of the average thickness from 20to150nm possess a grainlike structure with a lateral grain size of about 250nm. Such films reveal ferroelectric properties similar to KNbO3 single crystal. Temperature dependencies of optical second harmonic generation intensity show that the Curie temperature TC of the nanometer-thick KNbO3 films is about 30°C lower than the TC of KNbO3 single crystal, which is attributed to size effects in KNbO3 nanograins.

Magnetorefractive effect in manganites with a colossal magnetoresistance in the visible spectral region

The magnetotransmission, magnetoreflection, and magnetoresistance of the La0.7Ca0.3MnO3 and La0.9Ag0.1MnO3 epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.