Sr3Ru2O7 is a highly correlated narrow d-band metallic ferromagnet with a Curie temperature T-C = 105 K. Ca3Ru2O7, which is isomorphic to Sr3Ru2O7, becomes antiferromagnetic and remains metallic below T-N = 56 K and exhibits a lower-temperature transition at T-M = 48 K into a nonmetallic antiferromagnetic phase. Both systems have the Sr3Ti2O7 Staggered double-layered body-centered-tetragonal structure, Ca3Ru2O7 being less ideal because of the smaller Ca ionic radius. Both systems demonstrate avery high degree of anisotropy of the magnetic and electrical properties. Magnetization and magnetic susceptibility studies for 2 < T < 400 K and 0 < H < 7 T, electrical resistivity for 1 < T < 300 K, and heat capacity measurements for 1 < T < 20 K are presented on as-grown single crystals of (Sr1-xCax)(3)Ru2O7, spanning the full concentration range 0 less than or equal to x less than or equal to 1.0. The results show multiple magnetic phases, from ferromagnetism for x < 0.4 to antiferromagnetism for x > 0.4. The transition from ferromagnetism to antiferromagnetism precedes a crossover from metallic conductivity at low temperatures to nonmetallic conductivity for x > 0.7 and T less than or equal to 40 K. In all cases the resistivity at room temperature is large (rho approximate to 0.02-0.04 Ohm cm), but with a metallic temperature dependence (d rho/dT > 0), indicating the materials are probably ''bad'' metals. Resistivity anomalies at the transition temperatures suggest the oppening of a gap at the Fermi surface for the metallic antiferromagnetic phase (0.4 < x < 0.7). The gap appears to evolve smoothly with increasing Ca content and may be relevant to a Mott-like metal to nonmetal transition for Ca-rich samples, x less than or equal to 1.0. Magnetic anisotropy measurements show that the easy axis (c axis for x = 0) rotates into the ab plane with increasing Ca concentration and a lower-temperature canted magnetic structure is suppressed as the system becomes antiferromagnetic. The electronic component of the heat capacity, which is large for the end members of the (Sr1-xCax)(3)Ru2O7 series, gamma = 77 mJ/mole K-2 for x = 0 and gamma = 35 mJ/mole K-2 for x = 1.0, is even larger for most of the mixed systems, x not equal 0,1.0. The data are discussed relative to the physics of bad metals and to the highly correlated nature of the Ru-dominated narrow 4d bands. The results are compared with a recent analogous study of metallic ferromagnetism in single-crystal Sr1-xCaxRuO3. Included in this paper is a discussion of the strikingly strong variation between the magnetic and electrical properties of single-crystal materials compared to similar data from isostructural polycrystalline materials.
