Upper critical field anisotropy in BaFe2−xCoxAs

Abstract

The upper critical field was measured upto 12 T for three BaFe 2−x Co x As 2 single crystals with estimated Co concentrations of x = 0.082, x = 0.117 and x = 0.143. H C2 versus temperature was measured from temperature dependent resistivity, for various applied magnetic fields, H || ab and H || c. The [dH C2 /dT] T=Tc , normalized with the corresponding T C , decreases with increasing Co content, for both directions. The anisotropy γ defined as H C2 || ab / H C2 || c shows a distinct increase with Co content, and its temperature dependence shows a peak close to the T C . Magneto transport measurements, in the spin density wave regions, showed significant negative MR for H || ab and positive MR of H || c in the x = 0.082 sample. The implications of these results are discussed.

Magnetic scattering and electron pair breaking by rare-earth-ion substitution in BaFe2As2epitaxial films

“…1−x La x )Fe 2 As 2 film 3034.0 (±0.1) 1.75 (±0.05) 0.151 (±0.001) x film = 0.02 in (Ba 1−x La x )Fe 2 As 2 film 30 79.0 (±0.3) 1.25 (±0.06) 0.0740 (±0.001) x film = 0.08 in (Ba 1−x La x )Fe 2 As 2 film 30 98.7 (±0.0 decreases with increasing x film , while the γ values remain constant, which is consistent with the La-doping result that La doping increased the majority carriers (electrons) and decreased their mobilities. The MR became undetectable at higher x film values of 0.13-0.44, which is similar to the behavior of Ba(Fe 1−x Co x ) 2 As 2 single crystals[40]. On the other hand, in the cases of magnetic Ce and Pr doping, a negative MR appeared as x film increased.…”

Upper critical field and superconducting anisotropy of BaFe2-xRuxAs2(x=0.48 and 0.75) single crystals

“…The electron-doped BaFe 2 As 2 behaves similarly to the hole-doped system [15][16][17]26]. The doping dependences of γ reported for Co-substituted BaFe 2 As 2 are in general agreement with one another and suggest that γ is an increasing function of temperature [27,28] This γ (T) dependence appears to be similar in all the FeAs122 materials, independently of the carrier nature [23,24]. (x=0.48 and 0.75), where Ru doping does not affect the carrier density.…”

“…γ(T) shows a linear dependence, and valuable information of γ(T) can be obtained over a wide range of temperatures around 9 K with the same 14 T superconducting magnet. γ(T) of x=0.48 is 2.0 for 10 K and that of x=0.75 is 3.0 for 13 K, which are lower than γ =5-8 in the AFe x Se 2 and FeAs1111 system [21,22] but consistent with γ =2-3 in the electron-and hole-doped FeAs122 [14,15,28] and FeAs111 system [31]. γ decreases with decreasing temperature.…”

Observation of anomalous admixture of superconducting and magnetic fractions in BaFe2−xCoxAs2single crystals

“…The single crystals of BaFe 2−x Co x As 2 with x=0.10, 0.14, and 0.20 were prepared using self-flux method [34]. The bulk T c was identified from the onset of diamagnetism in a T dependent magnetization M (T) measurement at low H and also from the sharp drop in zero field resistance, R(T), data (T c 's are indicated by arrows in figures 1(a)-(c)).…”