Structural Distortion and Physical Properties in Double-Layered Ruthenate Sr_<3-x>Ca_xRu_2O_7(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We have investigated the structural, magnetic, and electronic properties of single-crystalline Sr_<3-x>Ca_xRu_2O_7 (0≤x≤3) grown by a floating-zone method. The results of X-ray diffraction, magnetic susceptibility, specific heat, and electrical resistivity measurements reveal that this system shows a novel phase diagram. With increasing Ca content, the enhanced paramagnetism of Sr_3Ru_2O_7 is suppressed, and a phase with a ferromagnetic correlation (0.5≲x≲1.2) emerges. This phase adjoins an antiferromagnetic two-dimensional metallic phase (1.2≤x≤3.0). At the border between these two phases, discontinuous changes in the lattice parameters are observed. In the ferromagnetically correlated phase, the density of states is significantly enhanced. In the antiferromagnetic phase, the magnetic easy axis changes continuously from the c-axis to the ab-plane with increasing Ca content. These magnetic and electronic properties are strongly coupled with structural distortions such as the rotation and tilting of the RuO_6 octahedra of this system.
2008-10-15