Magnetization studies have been carried out on a single crystal of TbBaCo 2 O 5.5 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 (T C = 277 K, T N1 = 210 K) and Tb (T N2 = 3.44 K) subsystems. It is shown that the spontaneous first-order phase transition at T N1 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 < 190 K for the Co subsystem and at T < T N2 for the Tb subsystem. The analysis of the magnetic properties of TbBaCo 2 O 5.5 points to the strongly anisotropic character of the Tb and Co subsystems. The Tb subsystem was shown to be of the Ising type. For this subsystem, the exchange interactions between nearest neighbours and next-nearest neighbours were determined. The observed properties of the Co subsystem also point to the Ising character of the Co ions. The effect of the twinning structure on magnetization processes of the weak ferromagnetic phase, especially hysteresis curves, is discussed.

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Magnetization of polycrystalline La1−xSrxMnO3 samples with x=0.13 and x=0.16 has been measured as a function of temperature and external magnetic field. Using the gathered data and the thermodynamic Maxwell’s relation, changes of the magnetic contribution to entropy under influence of the magnetic field, allowing to estimate the value of magnetocaloric effect, have been determined. The changes reach ∼7 J/(kg K) in the field of 7 T, which makes the studied samples good candidates for application for magnetic refrigeration. Expressions describing entropy and its change under influence of magnetic field have been derived in the molecular field approximation. Satisfactory agreement between the theoretical curves and the experimental dependencies has been found.

Recently, geometry-induced quantum effects in periodic nanostructures were introduced and observed. Nanograting has been shown to dramatically improve thermoelectric and electron emission properties, and originate a geometry induced doping or G-doping. Here, we concentrate on experimental investigation of G-doping. We fabricate nanograting (NG) layers and measure their electron transport properties. The grating was fabricated on the surface of a silicon on insulator (SOI) wafer device layer using laser interference lithography followed by reactive ion etching. Next, large square islands were shaped in the device layer.The characteristics of NG and plain islands were compared to investigate G-doping. Resistivity temperature dependences were recorded in the range of 4-300 K. For all 21 samples, the NG layers show a 2-3 order of magnitude reduction in resistivity with respect to the plain layer. Hall coefficient and thermopower measurements demonstrate that the NG layers are n-type. Obtained G-doping level corresponded to an "effective impurity" concentration of 10 18 cm À3 . The dependence of the resistivity and Hall coefficient on temperature and magnetic field were recorded in the ranges of 2-300 K and 0-3 T, respectively.