A. V. Kalinov,1,2,* O. Yu. Gorbenko,3 A. N. Taldenkov,4 J. Rohrkamp,2 O. Heyer,2 S. Jodlauk,2,5 N. A. Babushkina,4 L. M. Fisher,1 A. R. Kaul,3 A. A. Kamenev,3 T. G. Kuzmova,3 D. I. Khomskii,2 K. I. Kugel,6 and T. Lorenz2 1All-Russian Electrical Engineering Institute, Krasnokazarmennaya Str. 12, 111250 Moscow, Russia 2II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany 3Department of Chemistry, Moscow State University, 119991 Moscow, Russia 4Institute of Molecular Physics, Russian Research Center “Kurchatov Institute,” Kurchatov Square 1, 123182 Moscow, Russia 5Institut für Kristallographie, Universität zu Köln, Zülpicher Str. 49b, 50674 Köln, Germany 6Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Izhorskaya Str. 13, 125412 Moscow, Russia Received 22 July 2009; revised manuscript received 1 March 2010; published 21 April 2010

We present the study of magnetization, thermal expansion, specific heat, resistivity, and ac susceptibility of ${({\text{Pr}}_{1\ensuremath{-}y}{\text{Eu}}_{y})}_{0.7}{\text{Ca}}_{0.3}{\text{CoO}}_{3}$ cobaltites. The measurements were performed on ceramic samples with $y=0.12--0.26$ and $y=1$. Based on these results, we construct the phase diagram, including magnetic and spin-state transitions. The transition from the low-to-intermediate spin state is observed for the samples with $yg0.18$, whereas for a lower Eu-doping level, there are no spin-state transitions, but a crossover between the ferromagnetic and paramagnetic states occurs. The effect of oxygen isotope substitution along with Eu doping on the magnetic/spin state is discussed. The oxygen-isotope substitution ($^{16}\text{O}$ by $^{18}\text{O}$) is found to shift both the magnetic and spin-state phase boundaries to lower Eu concentrations. The isotope effect on the spin-state transition temperature $(yg0.18)$ is rather strong but it is much weaker for the transition to a ferromagnetic state $(yl0.18)$. The ferromagnetic ordering in the low-Eu-doped samples is shown to be promoted by the ${\text{Co}}^{4+}$ ions, which favor the formation of the intermediate-spin state of neighboring ${\text{Co}}^{3+}$ ions.

We study with O-17 NMR and bulk magnetization a lightly electron doped CaMnO3-x (x < 0.01) polycrystalline sample in the G-type antiferromagnetic state. The O-17 NMR spectra show two lines with very different intensities corresponding to oxygen sites with very different local magnetic environments. The more intense unshifted line is due to the antiferromagnetic (AF) matrix. The thermal dependence of the magnetic moment of the AF sublattice deduced from the O-17 linewidth is typical of insulating three-dimensional Heisenberg antiferromagnets. The less intense, strongly shifted line directly evidences the existence of ferromagnetic (FM) domains embedded in the AF spin lattice. The extremely narrow line in zero magnetic field indicates a nearly perfect alignment of the manganese spins in the FM domains which also display an unusually weak temperature dependence of their magnetic moment. We show that these FM entities start to move above 40 K in a slow-diffusion regime. These static and dynamic properties bear a strong similarity with those of a small size self-trapped magnetic polaron.

In a reel to reel MOCVD system YBCO films and buffer layers were deposited on textured NiW-tapes. The layers of all RTR MOCVD Coated Conductors were grown with excellent in plane and out of plane texture with FWHM of 5-7° and 1.4-4° respectively. The critical current densities of these films were up to 1 MA/cm2 at 77 K. MOCVD-YBCO films on MOD CeO2/LZO buffered NiW (delivered by FZ Karlsruhe) could be coated with critical current densities of up to 2 MA/cm2. The 'End to End' critical current of MOCVD-YBCO on MOD-LZO/NiW (delivered by Nexans Superconductors) was 58 A for a 700 nm thick film onto a 10 mm wide tape.

The 139La NMR spectra and spin–spin relaxation times have been measured for the 16O and 18O isotope-substituted manganite (La0.25Pr0.75)0.7Ca0.3MnO3 in the external magnetic field of 5 T. The NMR signal wipe-out has been observed in the 18O-enriched sample in the charge-ordered state. This phenomenon is connected with a sharp increase in the spin–spin relaxation rate. The great isotope-effect observed provides a clear evidence of an essential role of oxygen motion in controlling the long-range magnetic order in manganites.

We have investigated the effect of oxygen isotope substitution on the metal-insulator transition temperature and the resistivity of the narrow band manganite (La0.25Pr0.75)0.7Ca0.3MnO3 in a constant magnetic field. A set of 16 samples having different mixtures of 16O, 17O and 18O isotopes with average mass varying from 16.0 to 17.8 a.m.u. was studied. We have found that the magnetoresistance and the isotope effect can be linked together with a single parameter - effective magnetic field, which decreases linearly with an increase of average oxygen mass with a slope of -2 T/a.m.u. The applicability of the small polaron model is discussed.

In the paper, it is seen that many oxides can be obtained as thin epitaxial films in spite of the thermodynamic instability of corresponding bulk materials at the film deposition conditions. This synthetic approach, named epitaxial stabilization (ES), is based on free-energy gain due to structural coherence at the film/substrate interface and can be effectively used to enlarge the spectrum of new functional materials. A thermodynamic model of ES was developed and its validity was confirmed by the author's results on the stabilization of numerous rare earth compounds with garnet, perovskite and hexagonal structures in the form of epitaxial films obtained by metal-organic chemical vapor deposition (MOCVD) technique. The use of ES for selective epitaxy in the preparation of the planar structures is demonstrated.

A number of MIEC layers, La1-xSrxGa1-XFexO3 , Sr1-xLaxFe 1-xCoxO3 and La2NiO4, with a thickness 3–30 µm were obtained on the porous substrates by MOCVD. The film composition, microstructure and gas tightness were studied. Using postannealing with oxide fluxes the membranes of gas tightness high enough for application were obtained. Specific oxygen permeability of obtained membranes were measured.

The metal-organic (MO) CVD process was modified to allow the in-situ deposition of perovskite manganites on biaxially textured Ni-based metal tapes (RABiTS). The modification consists of the creation of the protective atmosphere by simultaneous introduction of ammonia and water. Such an atmosphere prevents the oxidation of Ni and the reduction of manganites into non-perovskite phases. MOCVD experiments were accomplished in the band-type reactor using the band evaporation system at 800degreesC and 850degreesC. Orthorhombic LaMnO3 film demonstrates (101) orientation (i.e. (001) orientation in cubic perovskite notation) minimizing lattice mismatch with the nickel substrate. The film stoichiometry, total pressure, water and ammonia flows greatly influence the quality of the film orientation. The oriented perovskite manganite films on Ni tapes can be used as buffers for high T. superconductors for high current applications as well as magnetoresistance-based sensors of the magnetic field.

We present and compare here transport measurements on epitaxial thin films of La2/3Ca1/3MnO3 grown by sputtering and MOCVD on SrTiO3 substrates. As-grown sputtered films exhibit depressed magnetic and transport properties when compared with MOCVD samples, but both magnetic transition temperature, TC, and saturation magnetization, MS, may be substantially improved by annealing samples in air. A transverse voltage drop is measured across a patterned measuring track with a temperature dependence that, particularly around TC, cannot be explained in terms of the longitudinal resistance component alone. High temperature annealing substantially suppress these features as well as the application of high magnetic fields. We argue that these effects reflect inhomogeneous current flow, likely to be related with charge inhomogeneities and electronic phase segregation.

Doped perovskite manganites Ln1−x(Ca,Sr)xMnO3 are characterised by strong interplay of electron, lattice and spin degrees of freedom. Its ground state ranges from antiferromagnetic insulator to a ferromagnetic metal and strongly depends on many parameters such as temperature, external field, chemical composition, oxygen isotope content, etc. In this work magnetic properties of the compound Sm1−xSrxMn16O3 together with its isotopically substituted counterpart Sm1−xSrxMn18O3 (90% of 18O2) were studied under magnetic field up to 35T in the temperature range 4–250K. We have performed magnetisation and susceptibility isothermal field scans alongside with study of transport properties. Several sharp magnetic phase transitions were observed, and H–T phase diagram was reconstructed. It was found that oxygen isotope substitution 16O→18O significantly modifies the phase diagram in such a way, that the transition fields shift up to the higher values in the samples with the heavier oxygen masses.

Transverse resistance measurements are reported on patterned epitaxial thin films of optimally doped La2/3Ca1/3MnO3 oxides. We show that the voltage drop measured across a micron-size patterned track displays a temperature dependence that, particularly in a temperature region around the Curie temperature, cannot be explained solely by the contribution of a longitudinal resistivity component. We argue that this response reflects inhomogeneous current flow, which sets in dramatically around the Curie temperature, likely related to charge trapping at microstructural defects. Indeed, we show that appropriate thermal annealing allows reducing to some extent their contribution. Thus we conclude that this experimental set-up allows for the monitoring of how electronic phase separation develops in optimally doped manganites. The impact of this effect on the determination of Hall coefficients is discussed.

We have found that the mentioned manganites exhibit not only CMR but also giant magnetostriction (MS) and both effects are interrelated and have identical nature, due to the phase segregation. Near the Curie point T-C we have observed a minimum of the temperature dependence of both negative MR, and negative volume MS. Their MS achieves a giant value (approximate to10(-3) at mu(0)H = 5 T). It is worth to notice that for Re = Sm and Eu-Nd compounds MR achieves a colossal value at low magnetic field (similar to70-80% at mu(0)H= 0.84 T). Besides, for Re = Sm, Tb-Nd and Eu-Nd compounds a sharp increase of volume MS and magnetization together with a sharp decrease of resistivity at some critical magnetic field mu(0)H(e) is observed in the T-C region. The value of mu(0)H(c) increases with temperature rise.

Magnetic, transport, magnetotransport, elastic and magnetoelastic properties of Re0.55Sr0.45MnO3 ceramic with fixed carrier concentration and tolerance factor but with different cation disorder parameter σ have been studied. A linear relation between TC and σ2 was found. Increase of σ leads to suppression of magnetoresistance and enhancement of volume change near TC. At T>TC sharp increase of magnetostriction and magnetization is observed at critical field HC, which increases with temperature rise. HC value, defined at fixed T/TC, decreases with σ.

EPR study of polycrystalline Sm1−xSrxMnO3 samples (x=0.40, 0.45, 0.50) within the temperature range 100–500K has revealed some details of its phase diagram. A change of the first-order ferromagnetic transition at TC≈130K (for x=0.40, 0.45) into the second-order one (for x=0.50) was clearly demonstrated. Analysis of the EPR line intensities reveal a charge ordering above 250K for all the compositions in spite of its short-range nature. For x=0.50 composition, a short-range antiferromagnetic ordering was also found below 170K. The latter might be responsible for suppression of the first-order type of the ferromagnetic transition.

This paper is a survey of recent author’s results obtained by the authors. It shows that many oxides can be obtained as thin epitaxial films in spite of their thermodynamic instability in bulk state at the film deposition conditions. This new synthetic approach, named epitaxial stabilization, is based on free energy gain due to structural coherence at the film/substrate interface. The epitaxial stabilization can be effectively used to enlarge the spectrum of new functional materials.

We report on the preparation and characterization of La1−xNaxMnO3 thin films grown by MOCVD on various single-crystalline substrates. Under appropriate conditions epitaxial thin films have been obtained. The Curie temperatures of the films, which are very similar to those of bulk samples of similar composition, reflect the residual strain caused by the substrate. The anisotropic magnetoresistance AMR of the films has been analyzed in some detail, and it has been found that it has a two-fold symmetry at any temperature. Its temperature dependence mimics that of the electrical resistivity and magnetoresistance measured at similar fields, thus suggesting that the real structure of the material contributes to the measured AMR besides the intrinsic component.

The effect of light of He-Ne (lambda = 633 nm) and Ar (lambda = 488 nm) lasers on the magnetization of epitaxial films of manganite Pr0.6La0.1Ca0.3MnO3 was studied. It has been found that the illumination stimulates the antiferromagnetic-ferromagnetic phase transition observed in this manganite in a magnetic field at low temperature. In a magnetic field, the light induces the magnetization increase that apparently is related to a partial transformation of an antiferromagnetic phase into a ferromagnetic one and a formation of ferromagnetic clusters within the antiferromagnetic phase. It was observed that a linearly polarized light effects stronger on the magnetic state of Pr0.6La0.1Ca0.3MnO3 films than an unpolarized light. A relaxation of the light-induced state was not defected. The photoexcited state is stable or a long-lived metastable one. [S0163-1829(99)01637-9].

Single crystals of CaGdAlO4 that have not been used previously as a substrate material for HTSC films were grown by Czochralski method and applied for the deposition of the Bi2Sr2CaCu2O8−x and LuBa2Cu3O7−z thin films. The main advantages of the CaGdAlO4 crystals are sufficiently low dielectric constant, appropriate crystal lattice match with most HTSC, fairly high crystal perfection and reproducibility of the growth process. Bi2Sr2CaCu2O8−x films were prepared by “off-axis” DC magnetron sputtering and LuBa2Cu3O7−z films were obtained by flash evaporation MOCVD technique on the (001) oriented CaGdAlO4 substrates.