Ruthenocuprates ${\mathrm{RuSr}}_2(\mathrm{E}\mathrm{u},\mathrm{C}\mathrm{e}{)}_2{\mathrm{Cu}}_2{\mathrm{O}}_{10-y}:$ Intrinsic magnetic multilayers

We report ac susceptibility data on ${\mathrm{RuSr}}_2(\mathrm{E}\mathrm{u},\mathrm{C}\mathrm{e}{)}_2{\mathrm{Cu}}_2{\mathrm{O}}_{10-y}$ (Ru-1222, Ce content $x=0.5\mathrm{}$ and 1.0), ${\mathrm{RuSr}}_2{\mathrm{GdCu}}_2{\mathrm{O}}_8$ (Ru-1212), and ${\mathrm{SrRuO}}_3.$ Both Ru-1222 $(x=0.5,$ 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic fields: logarithmic time relaxation, switching behavior, and “inverted” hysteresis loops. Neither Ru-1212 nor ${\mathrm{SrRuO}}_3$ exhibit such magnetic dynamics. The results are interpreted as evidence of the complex magnetic order in Ru-1222. We propose a specific multilayer model to explain the data, and note that superconductivity in the ruthenocuprate is compatible with both the presence and absence of the magnetic dynamics.