Electronic transport and antiferromagnetism in the layered compoundBaCoS2

Abstract

BaCoS 2 is a Mott insulator with a Neél temperature (T N ) close to room temperature. In the ordered antiferromagnetic phase, the magnetic moments are confined in the Co 2 S 2 planes, and arranged in alternatingly directed ferromagnetic chains. We report on resistivity and thermopower measurements and on roomtemperature cell constants of samples of BaCoS z with nominal sulfur content 1.9рzр2.1. We discuss the effect of sulfur content on cell constants and band filling. The main observation is a crossover from activated electronic transport at high temperatures, to high resistivity almost independent of temperature, and accompanied by a vanishingly small thermopower, at low temperatures ͑far below T N ͒. We interpret the transport mechanism in the low-temperature regime as tunneling in the Co 2 S 2 planes, to nearest neighbors along the ferromagnetic chains and to next-nearest neighbors in the perpendicular direction, or alternatively to nearest neighbors along the ferromagnetic chains with conducting inclusions acting as shorts.

Seebeck coefficient study on Mn-dopedYBa2Cu3O7Samuel1, Bai2, Sivakumar3 et al. 1999Phys. Rev. B16160View full textAdd to dashboardCite

“…12,15,25 The saddle point observed in the high resolution angle resolved photo emission experiments on the cuprate superconductors 10,48 point to a logarithmic density of states singularity ͑Van Hove singularity͒, close to the E f . Gasumyants et al 6 have attempted a quantitative estimation of the transport properties, under the narrow band considerations, using a few phenomenological parameters such as bandwidth (W D ), width of the conduction window (W ), and the degree of band filling (F).…”

“…33 Similar effects of hole depletion is observed in YBa 2 Cu 3 O 7Ϫ␦ samples with Pr doped at the Y site. 34 Fisher et al 25 have studied resistivity and thermopower of YBa 2 Cu 3Ϫx Co x O 7Ϫ␦ system and proposed the presence of a very narrow band near E f . Obertelli et al 9 have brought forth the close correlation existing between the thermoelectric power ͑TEP͒ and the superconductivity on several cuprate superconductors.…”

“…Several authors have reported Seebeck coefficients for several systems such as La 2Ϫx (Sr,Ba) x CuO 4 , 13,14 YBa 2 Cu 3 O 7Ϫ␦ ͑YBCO͒, 10,12,[15][16][17] Bi 2 Sr 2 Ca 1 Cu 2 O 8ϩy , [18][19][20] Tl 2 Ba 2 Ca 2 Cu 3 O y , 21,22 and HgBa 2 Ca 2 Cu 3 O 8ϩ␦ system, 23,24 and have analyzed the results obtained in the light of energy band calculations to understand the transport mechanism involved. 10,12,25,27 One of the established consensus on the YBa 2 Cu 3 O 7Ϫ␦ system is that the Cu 3d and O 2p orbitals in the vicinity of the Fermi energy (E f ) constitute the superconductivity in this system. This was supported by the angle resolved photoemission experiments [27][28][29] and the band calculations.…”

“…Over the decade, since the discovery of high-T c superconductors, study of transport properties has been a rich source for information on Fermi surface, complimented by theory 1-7 and experiments [8][9][10][11][12] alike. Compared to resistivity and Hall coefficient measurements, measurement of Seebeck coefficient is a powerful technique in probing the transport phenomena with minimal distortion arising from the defect structures, etc., which are not the characteristic of the sample studied.…”

Observation of a New Magnetic Anomaly below the Ferromagnetic Curie Temperature inYb14MnSb11

“…This compound was first synthesized by Chan et al [5], and it is isostructural with the Zintl compounds with the structure having 14 Yb 2 cations, an MnSb 9ÿ 4 tetrahedron, a Sb 7ÿ 3 unit, and 4 Sb 3ÿ anions. Initial studies on polycrystalline and single crystalline samples of this material indicated that the Mn magnetism is local in character with the exchange interaction between the well separated Mn 3 moments most likely due to conduction-electron mediated Rudermann-Kittel-Kasuya-Yoshida interactions [5,6]. The Curie temperature (T C ) is around 53 K, with robust ferromagnetic order setting in at low temperatures.…”