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The effect of treatment conditions on the magnetic and magnetotransport properties of A-site ordered PrBaMn2O6−δ manganites is examined. The parent oxygen-stoichiometric A-site ordered PrBaMn2O6 samples were prepared from oxygen-stoichiometric A-site disordered Pr0.50Ba0.50MnO3 ones by using a 'two-step' synthesis method. The most significant structural feature of the A-site ordered manganites is that the MnO2 sublattice is sandwiched by two kinds of rock-salt layers, PrOx and BaO. The oxygen-stoichiometric A-site ordered PrBaMn2O6 demonstrates a ferromagnetic metal to paramagnetic insulator transition with the Curie point at about 320 K. These compounds are stable in air up to 1300 °C. The A-site ordered PrBaMn2O6 samples were next reduced in flowing argon as well as being treated under high pressure conditions. The reduction of the A-site ordered PrBaMn2O6 samples leads to the appearance of an antiferromagnetic state with a Neel point of about 140 K, while the A-site order remains. Upon high pressure treatment the degree of A-site order decreases, which reduces TC to 180 K. The magnetotransport properties of A-site ordered manganites treated under different conditions are discussed in terms of the manganese valence, oxygen content and degree of A-site order.

Magnetic properties of detwinned Tb0.9Dy0.1BaCo2O5.5 single crystals have been studied. The admixture of Dy, introduced only for technological reasons, has no essential influence on the behaviour of the rare earth subsystem of this compound, which is determined by the electronic structure of the Tb3+ ions. It is shown that the Co3+ ions are Ising ions, with the easy axis along the a axis, in the temperature range 2–276 K (TC). The Tb3+ ions in the AFM phase (T

Magnetization studies have been carried out on a single crystal of TbBaCo2O5.5 in the temperature range 2–350 K and magnetic fields up to 50 kOe. Several spontaneous magnetic phase transitions have been observed and analysed in both Co (TC = 277 K, TN1 = 210 K) and Tb (TN2 = 3.44 K) subsystems. It is shown that the spontaneous first-order phase transition at TN1 from an antiferromagnetic to a weak ferromagnetic state is accompanied by an intermediate state. The properties of this state are strongly determined by the thermo-magnetic history of the sample. Metamagnetic type transitions have been observed at 140 K< T

Single crystals of La1−xBaxMn1−yCoyO3 (0.26 ≤ x ≤ 0.37; 0 ≤ y ≤ 0.31) perovskites were grown by the flux melt technique using the BaO–B2O3–BaF2 ternary system as a solvent. It was found that the cobalt content in the crystals is determined by the average oxidized state of the manganese ions and depends nonlinearly on the molar ratio of Co/Mn in the initial mixture. All the crystals exhibit ferromagnetic behaviour at low temperatures as well as a jump of resistivity and a magnetoresistance peak around the Curie temperature, gradually decreasing as the cobalt content increases. The low-temperature ferromagnetic phase transforms from the metallic to the semiconducting state with increase in cobalt content.

Magnetization reversal of a Fe/Si/Fe trilayer having a ferromagnetic bilinear and biquadratic exchange is investigated at 10 and 300 K. The experiments were performed using the magneto-optical Kerr effect technique and a SQUID magnetometer. The type of stable magnetic configuration is determined for both temperatures of the study. The hysteresis loops contain jumps in magnetization, which could be associated with the overcoming of the energy barriers related to the uniaxial anisotropy hard axes in the two iron layers. The analysis of the experimental results was performed in the framework of a model in which the ferromagnetic bilinear and biquadratic exchange between two magnetic layers separated by a nonmagnetic spacer and the cubic and uniaxial anisotropy were taken into account. Good qualitative agreement is obtained between the experimental and calculated field dependences of the magnetization.

Photoinduced changes of the field of the phase transition from the antiferromagnetic to the metamagnetic state have been found in the Ca3Mn2Ge3O12 garnet. This effect is interpreted as related to the experimentally detected photoinduced magnetic moment. The observed photoinduced effect persists during a long time at low temperatures.

We report on the seeded growth of large (up to 2?cm3) single crystals of the cubic and orthorhombic phases of Ba1-xKxBiO3. The shape of the crystals varies with potassium content from a cube to a cube-octahedron shape at x~0.2. The flux saturated by Bi2O3 alone with an anode potential of +740?mV were selected to grow cubic Ba1-xKxBiO3 crystals with x = 0.67, Tc~4.5?K. We found that a new cubic phase (x = 0.51, a = 4.266??) of crystals could be grown under +970?mV potential and reduced Bi2O3 content in the flux. The crystals grown at ~250??C acquired a cube-octahedron shape. In turn, crystals of the tetragonal Ba1.7K1.3Bi2O7 phase (a = 4.25??, c = 21.91??) up to several mm3 in size were grown at the same temperature but lower potential and higher Bi2O3 concentration in the flux. Surprisingly the crystals exhibited a weak superconductor-like magnetization.

The structure of a series of highly Al-doped superconducting Y(RE)-123 (RE = rare earth element) single crystals was investigated by XRD and NMR methods. On the basis of the data obtained by the structural investigations combined with the studies of magnetic and optical properties, the formation of various superstructures in the samples of pseudo-tetragonal symmetry has been discussed. The correlation between the carrier concentration and Tc-values has been determined. The superconductivity (at 70 K) was indicated even at the 2/3 and 1/3 Al substitution for Cu in the basal and CuO2 planes, respectively, in the phase presumably of a perovskite-like structural type.

The influence of In for Cr substitution on the para- to ferrimagnetic phase transition has been investigated for MnCr2-2xIn2xS4 spinel crystals by means of DC magnetization measurements. The critical exponents and calculated from the high field extrapolation of the modified Arrott plots were found to be unaltered with substitution and close to 3D Heisenberg ones. A considerable expansion of the temperature range of the upward curvature of the inverse initial susceptibility of the samples with disorder increase has been found. Non-monotonic temperature dependences of Kouvel-Fisher effective susceptibility exponent * for disordered samples and the increase of the * value with the In concentration growth were also observed.

The single crystals with two-leg spin-ladder–type structure were investigated. According to the structural, magnetic, optical and resistivity data obtained, the studied crystals [A2Cu2O3]5[CuO2]7 were shown, for the first time, to be high-Tc superconductors (Tc=80 K) which belong to the class of cuprates with incommensurate-type structure.

We report on the persistent photoinduced changes of intrinsic (critical temperature) and extrinsic (FC magnetization and width of the hysteresis loop) superconducting parameters of Tl2Ba2CaCu2O8 thin films. The relaxation back to the original state is very slow, being of the order of days at room temperature. Qualitatively the observed photoinduced changes may be considered as manifestations of two different types of photosensitive pinning centers in the investigated films.

Single crystals of La2CuO4 + δ were exposed to fast-neutron irradiation with fluences of 8.4 1016 n/cm2 and 3.65 1017 n/cm2 (E > 1 MeV). D.c. magnetization measurements of these samples were performed and compared with those of unirradiated samples to study the influence of irradiation-created defects on the magnetic properties of La2CuO4 + δ crystals. It was shown that the defects created by neutron irradiation can effectively limit the diffusion-controlled clustering process, therefore preventing the macroscopic phase separation. The results of our experiments well correspond with the prediction of the percolative phase separation model and give evidence of the existence of magnetic polarons in La2CuO4 + δ oxides.

The diamagnetic susceptibility χ of aligned carbon nanotubes is anisotropic: χ|| differs from χ⊥. The ratio χ||/χ⊥ exhibits a singularity at 40 K. Below this temperature χ|| differs in samples cooled in magnetic field from those cooled in zero field. This observation suggested interaction of the magnetic moments responsible for susceptibility.

Luminescence and structural properties of pure and Y-doped ZrO2 nanopowders with different Y content synthesized by co-precipitation of Zr and Y salts were investigated by x-ray diffraction, transmission electron microscopy, electron paramagnetic resonance (EPR) and photoluminescence (PL) methods. It was found that at constant calcination temperature (700 °С), the increase of Y content stimulates the transformation of crystalline phase from monoclinic through the tetragonal to the cubic one. Generally, room temperature PL emission was found to be similar for the samples with different Y content, demonstrating the same overlapped PL components in visible spectral range under extrinsic excitation. The relative contribution of each PL component was found to be affected by calcination time. In EPR spectra of as-prepared samples no signals were observed. The annealing in N2 or H2 flow results in the appearance of the signal from surface Zr3+ defects. In the latter the signal assigned to F-center also arises. The anti-correlation observed between the PL intensity and the value of the Zr3+ EPR signal allows us to conclude that the Zr3+ center is the center of fast non-radiative recombination. At the same time, interrelation between the intensity of the EPR signal assigned to F-centers and observed PL bands was not found.

Magnetization measurements for superconducting ceramics BiSrCaCu2Ox are reported. The critical temperature Tc=78 K and the critical fields Hc1=300 Oe and Hc2=150 kOe at 4.2 K are determined. Evaluations of the superconducting properties such as critical currents, the coherence length and the penetration depth are given.