arXiv subjects

Athena S. Sefat

Publications and source records attributed to Athena S. Sefat.

76 records · Page 5Linked to original sources

arXiv2008

Superconductivity at 22 K in Co-doped BaFe2As2 Crystals

Here we report bulk superconductivity in BaFe1.8Co0.2As2 single crystals below Tc = 22 K, as demonstrated by resistivity, magnetic susceptibility, and specific heat data. Hall data indicate that the dominant carriers are electrons, as expected from simple chemical reasoning. This is the first example of superconductivity induced by electron doping in this family of materials. In contrast to the cuprates, the BaFe2As2 system appears to tolerate considerable disorder in the FeAs planes. First principles calculations for BaFe1.8Co0.2As2 indicate the inter-band scattering due to Co is weak.

cond-mat.supr-con↗

arXiv2008

Superconductivity in Co-doped LaFeAsO

Here we report the synthesis and basic characterization of LaFe1-xCoxAsO for several values of x. The parent phase LaFeAsO orders antiferromagnetically (TN ~ 145 K). Replacing Fe with Co is expected to both electron dope the system and introduce disorder in the FeAs layer. For x = 0.05 antiferromagnetic order is destroyed and superconductivity is observed at Tconset = 11.2 K. For x = 0.11 superconductivity is observed at Tc(onset) = 14.3 K, and for x = 0.15 Tc = 6.0 K. Superconductivity is not observed for x = 0.2 and 0.5, but for x = 1, the material appears to be ferromagnetic (Tc ~ 56 K) as judged by magnetization measurements. We conclude that Co is an effective dopant to induce superconductivity. Somewhat surprisingly, the system appears to tolerate considerable disorder in the FeAs planes.

cond-mat.supr-con↗

arXiv2008

Electron Correlations in the Low Carrier Density LaFeAsO0.89F0.11 Superconductor (Tc = 28 K)

The crystal structure and numerous normal and superconducting state properties of layered tetragonal (P4/nmm) LaFeAsO, with F-doping of 11 %, are reported. Resistivity measurements give an onset transition temperature Tc = 28.2 K, and low field magnetic susceptibility data indicate bulk superconductivity. In applied magnetic field, analysis of the resistive transition results in a critical field Hc2 = 30 T and a coherence length 35 A. An upper limit for the electron carrier concentration of 1 x 10^21 cm-3 is inferred from Hall data just above Tc. Strong electron-electron correlations are suggested from temperature-dependent resistivity, Seebeck coefficient, and thermal conductivity data. Anomalies near Tc are observed in both Seebeck coefficient and thermal conductivity data.

cond-mat.supr-con↗

arXiv2006

The effect of hole-doping on the magnetic properties of Nd1-xTiO3

The magnetic properties of the hole(x)-doped Mott-Hubbard, antiferromagnetic insulator, NdTiO3, have been investigated in Nd1-xTiO3. For the materials in 0.010(6) < x < 0.112(4), correlation between the structural and magnetic properties is discussed with respect to the Ti - O - Ti angles and the Ti - O bond distances. For 0.010(6) < x < 0.071(10), long-range magnetic order is observed through low temperature neutron diffraction and heat capacity. Neel ordering temperatures of 88.2 K and 61.9 K are determined, respectively, for x = 0.019(6) and x = 0.064(10). From high resolution neutron diffraction, the Pnma magnetic structure is assigned, unambiguously, as GxCy on Ti3+ and Cy2 on Nd3+. The Ti3+ ordered moment decreases gradually from 0.45(8) uB for x = 0.019(6) to 0.31(7) uB for x = 0.071(10), but vanishes abruptly for higher x. Antiferromagnetic short-range order exists for 0.074(9) < x < 0.098(10) as determined by neutron diffraction and the field-dependence of the susceptibility. This is the first observation of short-range order for any hole-doped titanate system. For 29(4)% hole-doping in Nd1-xTiO3, x > 0.098(10), all magnetic ordering is destroyed.

cond-mat.str-el↗