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Te NMR studies were carried out for the bismuth telluride topological insulator in a wide range from room temperature down to 12.5 K. The measurements were made on a Bruker Avance 400 pulse spectrometer. The NMR spectra were collected for the mortar and pestle powder sample and for single crystalline stacks with orientations c parallel and perpendicular to field. The activation energy responsible for thermal activation. The spectra for the stack with c parallel to field showed some particular behavior below 91 K., Comment: 15 pages, 11 figures,1 table

We present the results of a comprehensive study of magnetic, magneto-transport and structural properties of nonstoichiometric MnxSi1-x (x=0.51-0.52) films grown by the Pulsed Laser Deposition (PLD) technique onto Al2O3(0001) single crystal substrates at T = 340{\deg}C. A highlight of our PLD method is the using of non-conventional (shadow) geometry with Kr as a scattering gas during the sample growth. It is found that studied films exhibit high-temperature (HT) ferromagnetism (FM) with the Curie temperature TC ~ 370 K accompanied by positive sign anomalous Hall effect (AHE); they also reveal the layered polycrystalline structure with a self-organizing grain size distribution. The HT FM order is originated from the bottom interfacial nanocrystalline layer, while the upper layer possesses the low temperature (LT) type of FM order with TC = 46 K, gives essential contribution to the magnetization below 50 K and is homogeneous on the nanometer size scale. Under these conditions, AHE changes its sign from positive to negative at T < 30 K. We attribute observed properties to the synergy of self-organizing distribution of MnxSi1-x crystallites in size and peculiarities of defect-induced FM order in PLD grown polycrystalline MnxSi1-x (x~0.5) films.

The Landau theory was applied to treat the phase diagrams for a multiferroic with two second order phase transitions taking into account the coupling of the primary order parameters with strain. Two order parameters are coupled biquadratically which corresponds to the magnetoelectric materials. The coupling with strain is assumed to be linear in strain and quadratic in order parameters. Three ordered phases are discussed. Analytic relationships were obtained for the phase transition temperatures and for elastic modulus changes through the phase transitions. Strong influence of the coupling with strain on the phase diagrams was shown., Comment: 9 pages, 4 figures; preprint of manuscript submitted to Physica B

23Na NMR studies of the Na-K eutectic alloy embedded into porous glass with 7 nm pores showed that melting of Na2K confined nanoparticles is a continuous process with smooth changes in the Knight shift of a narrow resonance line and nuclear spin relaxation between those in the crystalline and liquid states. The intermediate state which occurs upon melting is stable and more favorable than the liquid state. The inverse freezing transformation can be sharp as at a first order transition or continuous depending on the initial temperature of cooling. The results suggest revision of theoretical predictions for the melting and freezing transitions in confined geometry., Comment: 5 pages, 5 figures, preprint of manuscript submitted to Phys. Rev. B

Transport properties of GaAs/{\delta}/GaAs/In\timesGa1-\timesAs/GaAs structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content, are studied. In these structures DL is separated from QW by GaAs spacer with the thickness ds = 2-5 nm. All structures possess a dielectric character of conductivity and demonstrate a maximum in the resistance temperature dependence Rxx(T) at the temperature {\approx} 46K which is usually associated with the Curie temperature Tc of ferromagnetic (FM) transition in DL. However, it is found that the Hall effect concentration of holes pH in QW does not decrease below TC as one ordinary expects in similar systems. On the contrary, the dependence pH(T) experiences a minimum at T = 80-100 K depending on the spacer thickness, then increases at low temperatures more strongly than ds is smaller and reaches a giant value pH = (1-2)\cdot10^13 cm^(-2). Obtained results are interpreted in the terms of magnetic proximity effect of DL on QW, leading to induce spin polarization of the holes in QW. Strong structural and magnetic disorder in DL and QW, leading to the phase segregation in them is taken into consideration. The high pH value is explained as a result of compensation of the positive sign normal Hall effect component by the negative sign anomalous Hall effect component., Comment: 19 pages, 6 figures

The photoconductivity of GaAs structures delta-doped by Sn has been investigated for wavelengths lambda= 650-1200 nm in the temperature interval T= 4.2-300 K. The electron densities and mobilities, before and after illumination, have been determined by magnetoresistance, Shubnikov-de Haas effect and Hall effect measurements, in high magnetic fields. For the heavily doped structures (n_H> 2x10^13 cm^-2) we observe under illumination by light with wavelengths larger than the band-gap wavelength of the host material (lambda= 815 nm at T= 4.2 K) first positive (PPPC) and then negative (NPPC) persistent photoconductivity. The NPPC is attributed to the ionisation of DX centres and PPPC is explained by the excitation of electrons from Cr impurity states in the substrate. For lambda< 815 nm in addition the excitation of electron over the band gap of GaAs contributes to the PPPC. For the lightly doped structures (n_H<= 2x10^13 cm^-2) the photoconductivity effect is always positive., Comment: 17 pages (includes 6 figures); Postscript file; Semicond. Sci. Technol. in print

We have prepared a number of GaAs structures delta-doped by Sn using the well-known molecular beam epitaxy growth technique. The samples obtained for a wide range of Sn doping densities were characterised by magnetotransport experiments at low temperatures and in high magnetic fields up to 38 T. Hall-effect and Shubnikov-de Haas measurements show that the electron densities reached are higher than for other delta-dopants, like Si and Be. The maximum carrier density determined by the Hall effect equals 8.4x10^13 cm^-2. For all samples several Shubnikov-de Haas frequencies were observed, indicating the population of multiple subbands. The depopulation fields of the subbands were determined by measuring the magnetoresistance with the magnetic field in the plane of the delta-layer. The experimental results are in good agreement with selfconsistent bandstructure calculations. These calculation shows that in the sample with the highest electron density also the conduction band at the L point is populated., Comment: 11 pages text (ps), 9 figures (ps), submitted to Semicon. Science Techn