Abstract
We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se–doping produces several effects: it suppresses semiconducting–like behavior observed in the undoped Sr0.5Ce0.5FBiS2, the ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and the superconducting transition temperature, Tc, gets enhanced slightly to 2.9–3.3 K. Thus in these Se–doped materials, TFM is marginally higher than Tc. Magnetization studies provide evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex at x ≥ 0.5 in contrast to the undoped Sr0.5Ce0.5FBiS2 (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce–moment (~2.2 μB), the ferromagnetically ordered Ce–moment in the superconducting state is rather small (~0.1 μB) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr0.5Ce0.5FBiS2-x Sex (x = 0.5 and 1.0) are distinctive Ce–based bulk superconducting itinerant ferromagnetic materials with Tc < TFM. Furthermore, a novel feature of these materials is that they exhibit a dual and quite unusual hysteresis loop corresponding to both the ferromagnetism and the coexisting bulk superconductivity.
Highlights
We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2
U–5f itinerant electrons are responsible for both superconductivity and ferromagnetism
Ferromagnetism and superconductivity have been reported to coexist in CeO1-x FxBiS2 and Sr1-xCexFBiS2 with Tc ~ 2.5–4 K and TFM ~4–8 K20,27,52–54
Summary
We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. U–5f itinerant electrons are responsible for both superconductivity and ferromagnetism These materials, with TFM >TSC, present an unusual and surprising scenario of coexistence, namely, superconductivity setting in an already ferromagnetically ordered host. In such cases, spin-triplet pairing (p-wave superconductivity) has been suggested (U-compounds such as UCoGe, URhGe and UGe2 have been proposed/ considered p-wave ferromagnetic superconductors)[14] to be compatible with itinerant ferromagnetism. Ferromagnetism and superconductivity have been reported to coexist in CeO1-x FxBiS2 and Sr1-xCexFBiS2 with Tc ~ 2.5–4 K and TFM ~4–8 K20,27,52–54 As these materials have layered structure, magnetism originates in the Ce−O (or Sr/Ce−F) layers and conduction occurs in BiS2 layers. Our observation of the coexistence of superconductivity and itinerant ferromagnetism in Sr0.5Ce0.5FBiS2-xSex is a timely discovery, in that it puts U- and Ce on equal footing in this respect
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