Weak ferromagnetism in two-dimensional bilayered Sr3-xCaxRu2O7

We have synthesized a bilayered ruthenate solid solution Sr3-xCaxRu2O7 (0 less than or equal to x less than or equal to 2.0), which is homologous to the copper-free layered-perovskite superconductor Sr2RuO4 (T-c=1.5 K). The x dependence of the lattice parameters, magnetic susceptibility chi(T), magnetization M(H), and electrical resistivity rho(T) is systematically examined. Samples for all x show magnetic ordering below 150 K, It is shown, however, that the magnetic correlations change with increasing Ca content. The lowest ferromagnetic-ordering temperature in this series is observed at 3.2 K in the sample with x(Ca)=1.0. This transition is described well as a weakly ferromagnetic ordering by self-consistent renormalization (SCR) theory of spin fluctuations. To the best of our knowledge, this is the first example of applying the SCR theory to a weak ferromagnet with a quasi-two-dimensional layered crystal structure. [S0163-1829(98)00502-5].