M. G. Mikheev

Evidence for a two-band behavior of MgB2 from point-contact and tunneling spectroscopy

Ya. G. Ponomarev, S. A. Kuzmichev, M. G. Mikheev, M. V. Sudakova, S. N. Tchesnokov, N. Z. Timergaleev, A. V. Yarigin, M. V. Lomonosov Moscow State University, Department of Physics, 119899 Moscow, Russia, E. G. Maksimov, S. I. Krasnosvobodtsev and A. V. Varlashkin, P. N. Lebedev Physics Institute, RAS, Moscow, Russia, M. A. Hein, G. Müller, H. Piel, Bergische Universität Wuppertal, Fachbereich Physik, D-42097 Wuppertal, Germany, L. G. Sevastyanova, O. V. Kravchenko, K. P. Burdina, B. M. Bulychev, M. V. Lomonosov Moscow State University, Department of Chemistry, 119899 Moscow, Russia.

Synthesis and crystal structure of the Sr2Al1.07Mn0.93O5 brownmillerite

A new brownmillerite-type compound Sr2Al1.07Mn0.93O5 was synthesized. The crystal structure was determined using electron diffraction and high resolution transmission electron microscopy and refined from X-ray powder diffraction data (space group Imma, a = 5.4358(1) A, b = 15.6230(4) A, c = 5.6075(1) A, RI = 0.036, RP = 0.023). The structure is characterized by a disordered distribution of the tetrahedral chains in L and R configuration and a partial occupation of the octahedral position by the Mn3+ and Al3+ cations. The relationships between the crystal structures of Sr2Al1.07Mn0.93O5 and its A2B′MnO5 analogues (A = Ca, Sr, B′ = Al, Ga) and the structural reasons for the different types of tetrahedral chain ordering in brownmillerites are discussed. The temperature dependences of the magnetic susceptibility and specific heat reveal that the compound is antiferromagnetically ordered below TN = 105 K.

Synthesis and crystal structure of the Sr_{2}Al_{1.07}Mn_{0.93}O_{5} brownmillerite

A new brownmillerite-type compound Sr2Al1.07Mn0.93O5 was synthesized. The crystal structure was determined using electron diffraction and high resolution transmission electron microscopy and refined from X-ray powder diffraction data (space group Imma, a = 5.4358(1) A, b = 15.6230(4) A, c = 5.6075(1) A, RI = 0.036, RP = 0.023). The structure is characterized by a disordered distribution of the tetrahedral chains in L and R configuration and a partial occupation of the octahedral position by the Mn3+ and Al3+ cations. The relationships between the crystal structures of Sr2Al1.07Mn0.93O5 and its A2B′MnO5 analogues (A = Ca, Sr, B′ = Al, Ga) and the structural reasons for the different types of tetrahedral chain ordering in brownmillerites are discussed. The temperature dependences of the magnetic susceptibility and specific heat reveal that the compound is antiferromagnetically ordered below TN = 105 K.

New antiferromagnetic semiconductor CuCr1 5Sb0 5S4

Abstract The magnetic, electric and crystallographic properties of the new compound with the spinel structure CuCr 1.5 Sb 0.5 S 4 were studied. It appears that this compound, being a non-degenerate p-type semiconductor, has magnetic properties typical of antiferromagnets: a linear magnetic field dependence of the magnetization and a maximum of the magnetic susceptibility at temperature T N = 28 K. Also, the lattice parameter a , the anion parameter u and the temperature factors are presented. The distances between cations (both in the tetrahedral and octahedral positions) and anions show that between anions and cations in tetrahedral positions, the covalent bond dominates and between anions and cations in octahedral positions, the ionic bond dominates.

Multiple Andreev Reflections Spectroscopy of Two-Gap 1111- and 11 Fe-Based Superconductors

Using the “break-junction” technique, we prepared and studied superconductor–constriction–superconductor (ScS) nanocontacts in polycrystalline samples of Fe-based superconductors CeO0.88F0.12FeAs (Ce-1111;

Investigation of a superconducting Mg1−xAlxB2 system by tunneling and microjunction (Andreev) spectroscopies

T_{C}^{\mathrm{bulk}} = 41 \pm1~\mathrm{K}

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

), LaO0.9F0.1FeAs (La-1111;

Leggett’s mode in Mg1−x AlxB2

T_{C}^{\mathrm{bulk}} = 28 \pm1~\mathrm {K}

Andreev spectroscopy of iron-based superconductors: temperature dependence of the order parameters and scaling of

), and FeSe (

\Delta_{\rm L, S}

T_{C}^{\mathrm{bulk}} = 12 \pm1~\mathrm{K}