Observation of a Metallic Antiferromagnetic Phase and Metal to Nonmetal Transition inCa3Ru2O7

Abstract

Single crystal ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ shows a metallic antiferromagnetic phase intermediate between a first-order metal to nonmetal transition at $T_M=48\mathrm{}\mathrm{K}$ and the antiferromagnetic ordering (Néel) temperature, $T_N=56\mathrm{}\mathrm{K}$. The metallic antiferromagnetic phase is predicted within various Mott-Hubbard models. Magnetization and electrical resistivity reveal strongly anisotropic metamagnetism in the nonmetallic antiferromagnetic phase. The charge and spin excitations are strongly coupled: The $H-T$ phase diagrams determined by magnetization and magnetoresistivity are indistinguishable and reveal a multicritical point. The heat capacity of ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ suggests it is a highly correlated electron system.