Effects of Co doping on the transport properties and superconductivity in CeFe_{1 −x}Co_xAsO

Abstract

A series of CeFe(1-x)Co(x)AsO oxyarsenide compounds with Co doping on iron sites (x = 0-0.2) have been synthesized by a solid state reaction method. The effects of Co doping on the electrical transport properties and superconductivity were analyzed with a special emphasis on the analysis of thermopower. Undoped CeFeAsO shows an electrical resistivity anomaly at about 150 K, which was ascribed to a spin-density-wave (SDW) instability. This anomaly is suppressed and a superconducting transition occurs at T(c) = 3.2 K in CeFe(0.95)Co(0.05)AsO, the maximum superconducting transition temperature (T(c)) of 12.5 K is observed in CeFe(0.90)Co(0.10)AsO, and the thermopower is increased by the Co doping. As has been previously suggested, the emergence of superconductivity seems to be closely linked to the thermopower, and there is a close correlation between T(c) and the thermopower, both showing a similar dome-like doping dependence.

Magnetocrystalline anisotropic effect inGdCo1−xFexAsO(x=0,0.05)

“…In the Ce(Fe,Co)AsO series, superconductivity appears while the magnetic order at T Fe N is quickly suppressed upon substituting Fe with Co. 14,15 The Ce Néel temperature slightly increases near the Fe-3d magnetic instability, but shows a nearly unchanged value on further increasing the Co concentration, 14 indicating a strong coupling between Ce 4f electrons and Fe 3d electrons in CeFeAsO, as previously reported by neutron scattering and muon spin relaxation measurements. 16,17 On the Co-rich side, the ferromagnetically ordered Co ions have a strong polarization effect on the AFM order of Ce moments.…”

“…9,10 Elemental substitutions in CeFeAsO, e.g., Fe/Co or As/P, may induce superconductivity while suppressing the magnetic order of Fe-3d electrons. [11][12][13][14][15] On the other hand, CeFePO is a paramagnetic (PM) heavy fermion metal. 1 Evidence for a magnetic quantum phase transition was shown in CeFeAs 1−x P x O, where the AFM state is separated from the PM heavy fermion state, and a ferromagnetic order develops in the intermediate doping region.…”

Tunable interplay between3dand4felectrons in Co-doped iron pnictides

“…Upon substituting Fe with Co, the magnetic/structural transition is quickly suppressed and superconductivity exists over a narrow doping range. [15][16][17][18][19] In the ReO layers, partial substitution of Gd with Th suppresses the magnetic/structural transition and then gives rise to superconductivity where T sc reaches a maximum of 56 K at 20% Th. 5 Similarly, a narrow superconducting region was also observed in GdFeAsO 1−δ by introducing oxygen deficiency.…”

Ferromagnetism and superconductivity in CeFeAs1−xPxO (Jesche1, Förster2, Spehling3 et al. 2012Phys. Rev. B

“…This is a very general property of the Fe-based superconductors and in fact there are only a few examples known where SC does not show up despite vanishing Fe ordering [e.g., Mn-doped LaFeAsO 7 or BaFe 2 As 2 8 ]. In this sense CeFeAs 1−x P x O presents a unique situation because of the following: First, replacing As with P "usually" results in SC as shown for AFe 2 As 2 [A = Ca, 9 Ba, 10 Sr, 9 Eu 11 ] and RFeAsO [R = La, 5 Sm 12 ], and second, CeFeAsO becomes superconducting when substituting Fe with Co 13 or O with F 14 and also by inducing oxygen vacancies. 2 But combining P doping with R = Ce among the RFeAsO compounds results in exceptional behavior: The Fe ordering is suppressed, as shown by de la Cruz et al 15 and Luo et al, 16 however, superconductivity had not yet been observed in CeFeAs 1−x P x O.…”

“…13,14 Therefore, the origin for this behavior is more complex than a possible simple sign change of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and will hopefully stimulate further theoretical investigations. For x > 70% the FM ordering of Ce becomes weaker, and for x = 90%, T C is reduced to 2.7 K. P concentrations of 90% < x 100% result in further suppression of T C , which will be the focus of a forthcoming publication.…”