P. Starowicz

The surface and domain structure of NbTe2

Scanning tunneling microscopy of freshly cleaved NbTe2 van der Waals surfaces reveals that Te vacancies regularly appear in the topmost chains of the Te surface layer. As a result of reduced symmetry with regard to the parent CdI2 structure microdomains of three possible orientational variants are formed, separated by ortho (601)- or meta (1201)boundaries, while the para (1801)-boundaries are not detected. Regions close to the boundaries are often modulated with periodicities of the adjacent domains, confirming that the boundaries in neighboring Te–Nb–Te triple layers do not necessarily coincide. r 2002 Elsevier Science B.V. All rights reserved.

Magnetic structures of Tb2Co3Si5 and Dy2Co3Si5 compounds

Abstract Neutron diffraction studies indicate that polycrystalline R 2 Co 3 Si 5 (R=Tb and Dy) intermetallic compounds with monoclinic Lu 2 Co 3 Si 5 -type crystal structure have different magnetic structures. Tb 2 Co 3 Si 5 has a sine wave modulated structure described by the wave vector k =(0, 0.0817(6), 0) in the temperature range 1.6 K– T N =22.6 K while for Dy 2 Co 3 Si 5 a collinear antiferromagnetic structure is observed between 1.5 K and T N =21.9 K. For R=Tb the magnetic moment is parallel to the c -axis while for R=Dy it forms an angle of 25.8° with the c -axis.

Crystal and magnetic structures of Nd2Ni2Sn and Dy2Ni2Sn compounds

Abstract Neutron diffraction and magnetometric measurements on polycrystalline samples of Nd2Ni2Sn and Dy2Ni2Sn compounds were performed in the temperature range between 1.5 and 293 K. Both compounds have the orthorhombic crystal structure similar to the W2CoB2-type. In both compounds at T=1.5 K the rare earth moments form noncollinear magnetic structures with ferro- and antiferro-components. With increasing temperature changes from the noncollinear magnetic structure to a ferromagnetic one for Nd2Ni2Sn at 15 K and to an antiferromagnetic one for Dy2Ni2Sn at 28.1 K are observed. The transition to the paramagnetic state appears at 19.5 and 49.4 K for Nd2Ni2Sn and Dy2Ni2Sn, respectively.

Mechanisms of electrical conductivity in Y1−xCaxBa2Cu3O6.1 system

Abstract Systematic studies of transport properties in deoxygenated Y 1− x Ca x Ba 2 Cu 3 O 6.1 series allowed to propose a diagram of conductivity mechanisms for this system. At intermediate temperature a variable range hopping (VRH) in two-dimensions prevails. At lower temperature VRH in the presence of a Coulomb gap for smaller x and VRH in two-dimensions for larger x are found. In a vicinity of superconductivity we observe conductivity proportional to T . Thermally activated conductivity dominates at higher temperature. This diagram may be universal for the whole family of undoped high T c related cuprates.