Identification of the muon stopping sites in GdSr2Cu2RuO8: Confirmation of ferromagnetic cuprate planes in a superconducting cuprate

► The Ru spins in GdSr2Cu2RuO8 are ordered antiferromagnetically along the c-axis. ► The cuprate planes are ordered ferromagnetically in the a-b plane and are stacked antiferromagnetically. ► Muons stopped in the center of the ferromagnetic CuO2 planes will experience an induction of ∼725 G. ► The calculated results are in close agreement with two independent experiments.