Magnetosuperconductivity in ruthenocuprates RuSr2GdCu2O8(Ru 1212) and RuSr2(Gd0.75Ce0.25)2Cu2O10 (Ru 1222) a critical review

TL;DR

This review discusses the complex coexistence of magnetism and superconductivity in ruthenocuprates Ru-1212 and Ru-1222, highlighting experimental challenges, contradictory findings, and the need for further conclusive evidence of their intrinsic properties.

Contribution

It provides a comprehensive critical review of experimental results, contradictions, and the current understanding of magneto-superconductivity in ruthenocuprates, emphasizing unresolved issues.

Findings

Superconductivity coexists with magnetic order in ruthenocuprates.

Oxygen content control is challenging, especially in Ru-1212.

Microscopic coexistence of magnetism and superconductivity remains unconfirmed.

Abstract

We reviewed our various results on rutheno-cuprate magneto-superconductors RuSr2GdCu2O8(Ru-1212) and RuSr2(Gd0.75Ce0.25)2Cu2O10(Ru-1222). It is observed, that it is difficult to control the oxygen content of Ru-1212, though the same is possible up to some extent for Ru-1222. Samples of both phases exhibited superconductivity, presumably in the CuO2 plane at low temperatures coexisting with magnetic ordering of Ru spins of predominantly antiferromagnetic type below 140 K having a ferromagnetic component appearing below 20 K. Electrical conductivity measurements indicate that the RuO2 layer takes part in conduction besides the CuO2 plane. The magnetic ordering temperature of Ru spins is seen as a clear hump in the resistivity measurements, establishing the magnetic spins interaction with the conduction carriers. Though the bulk physical property measurements exhibited the magneto-superconductivity, SAED results question the same to co-existence of the two at microscopic level. Our results indicate towards the fact that solid solutions of (Ru1-xCux)-1212, which can be superconducting with x > 0.5, but not magnetic may be precipitating with the stoichiometric magnetic Ru-1212 phase. Also highlighted in the review are various existing contradictions in the literature regarding physical properties of these systems. One such example is the results for Cp that are used as the evidence of bulk superconductivity in Ru-1212. We believe the establishment of superconductivity along with low-T ferromagnetic ordering of Ru spins in intrinsically phase-pure rutheno-cuprates is yet far from conclusive.