Spin-charge coupling for dilute La-dopedCa3Ru2O7

Abstract

${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ is a Mott-like system with a narrow gap (\ensuremath{\approx}0.1 eV). Very dilute doping of trivalent La (\ensuremath{\leqslant}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 ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}.$ The antiferromagnetic metallic phase unique to ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ persists into $({\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{)}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ 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 ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ is much more drastic than that of Sr doping, implying the importance of the added electron from the La ion. Unlike ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ where ferromagnetism is instantly induced in the antiferromagnetic host by La doping, ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ shows no ferromagnetic ordering when La doped, but readily becomes a ferromagnet in modest magnetic fields.