Tuning the competing phases of bilayer ruthenate C a3 R u2 O7 via dilute Mn impurities and magnetic field

We have systematically investigated the evolution of the magnetic structure of the bilayer ruthenate Ca3(Ru1-xMnx)2O7 induced upon Mn doping. For 0<x≤0.03, the materials exhibit the same spin structure as that of the parent compound at low temperature, while an incommensurate cycloidal magnetic structure emerges at T slightly above the metal-insulator transition (MIT) temperature (TMIT). In contrast, for x≥0.04 the ground state becomes a G-type antiferromagnetic Mott insulator. Furthermore, we have observed magnetic-field-induced transitions in Ca3(Ru0.96Mn0.04)2O7, which is positioned at the phase boundary. Below TMIT, the magnetic transition is accompanied by a structural transition, as well as a dramatic change in the electronic properties from a Mott insulator to a localized phase. On the contrary, an incommensurate-to-commensurate spin structure transition is observed for TMIT<T<TICM. Our results suggest strong competing magnetic tendencies in this bilayer ruthenate system that are very susceptible to 3d transition-metal substitution and magnetic field.