Ferromagnetic correlations in bilayered Sr_<3-x>Ca_xRu_2O_7
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We have synthesized a new bilayered ruthenate solid solution Sr3-xCaxRu2O7 (0≤x≤2.0), which is homologous to copper-free layered perovskite superconductor Sr2RuO4 (Tc=1.5 K), with the aim of searching for new superconductors. We have also succeeded in growing single crystals of Sr3Ru2O7 by a floating zone (FZ) method. A systematic measurement has been carried out for the x dependence of the lattice parameters, magnetic susceptibility x(T), magnetization M(H), and electrical resistivity p(T). No indication of superconductivity has been observed down to 100 mK for x=0 (single crystals), 300 mK for x=1, and 2 K for other compositions. The measured values of lattice parameters and of magnetic quantities for the present single crystal samples are in good agreement with those for polycrystalline samples. Polycrystalline samples for 0.6<x≤2.0 show magnetic ordering below 50 K. It is intriguing that the magnetic correlations vary with increasing Ca content, from nearly ferromagnetic, to itinerant weakly ferromagnetic, and finally to localized antiferromagnetic. For x(Ca)=0, we have concluded that the ground state is the strongly-correlated Fermi liquid accompanied by enhanced ferromagnetic correlations. The lowest magnetic 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 that due to a weakly ferromagnetic ordering by the self-consistent renormalization (SCR) theory of spin fluctuations. To the best of our knowledge, this is the first example to demonstrate an applicability of the SCR theory to a weak ferromagnet with a quasi-two dimensional crystal structure.
Chapter1.Introduction / p1
Chapter2.Experimental / p4
2.1 Sample preparation and characterization / p4
2.2 Measurements / p6
Chapter3.Phase diagram of Sr3-xCaxRu₂O₇ / p7
3.1 Lattice parameters and oxygen content / p7
3.2 Resistivity / p9
3.3 Magnetic susceptibility / p9
3.4 AC magnetization / p12
3.5 Magnetization curves / p13
3.6 Phase diagram / p15
Chapter4.Sr₃Ru₂O₇:nearly ferromagnetic metal / p16
Chapter5.Sr₂CaRu₂O₇:weakly ferromagnetic metal / p22
Chapter6.Conclusions / p26
Acknowledgments / p27
References / p28
Copyright(c) by Author
(1) Weak ferromagnetism in two-dimensional bilayered Sr3-XCaxRu2O7. S. Ikeda, Y. Maeno, and T. Fujita. Physical Review B, 57(2), 978-986 (1998).
(2) Two Distinct Structural Phases in Sr3-xCaxRu2Oy. S. Ikeda, Y. Maeno, H. Muranishi, and T. Fujita. Journal of Low Temperature Physics, 105(5/6), 1599-1604 (1996).