Upper critical field of the magnetic superconductor RuGd1.4Ce0.6Sr2Cu2O10-Φ

We performed measurements of magnetic susceptibility, electrical resistivity, and magnetoresistance in magnetic fields of up to 18 T in the magnetic superconductor RuGd 1 . 4 Ce 0 . 6 Sr 2 Cu 2 O 1 0 - Φ synthesized in oxygenpressures up to 95 atm. The magnetic-susceptibility data show the occurrence of an antiferromagnetic state below T N ∼ 175 K, followed by the development of a weak ferromagnetic state near T M ∼100 K, and followed further by the onset of superconductivity (SC) at T c ∼42 K. The electrical resistivity as a function of temperature shows an evolution from nonmetal-to-SC behavior in samples prepared in a flux of O 2 to a well defined metal-like behavior in samples prepared under 95 atm pressure of O 2 . The electron-phonon coupling constant was calculated from transport data to be λ t r ∼0.17, a value comparable with other cuprates, indicating weak electron-phonon coupling in these ruthenates. The values of the upper critical field H c 2 for the O 2 high-pressure treated samples were obtained from the magnetoresistivity data yielding H a b c 2 (0)∼39 T, and the out-of-plane superconducting coherence length ξ c (0)∼28 A. Based on the similarities between these ruthenates and the superconductor YBa 2 Cu 3 0 7 _,S, we estimated H c c 2 (0)∼8 T and ξ a b (0)∼140 A. We used these parameters to discuss the coexistence of long-range magnetic order and superconductivity on a microscopic scale on these materials.