Spin-charge coupling for dilute La-doped Ca3Ru2O7

Ca3RU2O7 is a Mott-like system with a narrow gap (approximate to 0.1 eV). Very dilute doping of trivalent La (less than or equal to 5%) for divalent Ca prompts rapid and simultaneous changes in both the magnetic and transport properties, unambiguously illustrating the strong spin-charge coupling that characterizes Ca3Ru2O7. The antiferromagnetic metallic phase unique to Ca3Ru2O7 persists into (Ca1-xLax)(3)Ru2O7 with x = 0.04, which is followed by a fully metallic ground state with a quenching of the magnetic moment at x = 0.05. A large sudden drop in the magnetoresistivity up to 20 T defines a transition that is highly hysteretic and becomes irreversible at low temperatures and with La doping. The impact of La doping on Ca3RU2O7 is much more drastic than that of Sr doping, implying the importance of the added electron from the La ion. Unlike Ca2RuO4 where ferromagnetism is instantly induced in the antiferromagnetic host by La doping, Ca3Ru2O7 shows no ferromagnetic ordering when La doped, but readily becomes a ferromagnet in modest magnetic fields.