Abstract
We have carried out detailed magnetic and transport studies of the new Sr(0.5)Ce(0.5)FBiS(2-x)Se(x) (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr(0.5)Ce(0.5)FBiS(2). Se-doping produces several effects: it suppresses semiconducting-like behavior observed in the undoped Sr(0.5)Ce(0.5)FBiS(2), the ferromagnetic ordering temperature, T(FM), decreases considerably from 7.5 K (in Sr(0.5)Ce(0.5)FBiS(2)) to 3.5 K and the superconducting transition temperature, T(c), gets enhanced slightly to 2.9-3.3 K. Thus in these Se-doped materials, T(FM) is marginally higher than T(c). Magnetization studies provide evidence of bulk superconductivity in Sr(0.5)Ce(0.5)FBiS(2-x)Se(x) at x ≥ 0.5 in contrast to the undoped Sr(0.5)Ce(0.5)FBiS(2) (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce-moment (~2.2 μ(B)), the ferromagnetically ordered Ce-moment in the superconducting state is rather small (~0.1 μ(B)) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr(0.5)Ce(0.5)FBiS(2-x) Se(x) ((x) = 0.5 and 1.0) are distinctive Ce-based bulk superconducting itinerant ferromagnetic materials with T(c) < T(FM). 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.