From quasi-2D metal with ferromagnetic bilayers to Mott insulator with G-type antiferromagnetic order in Ca$_{3}$(Ru$_{1-x}$Ti$_{x}$)$_{2}$O$_{7}$

Ca$_{3}$Ru$_{2}$O$_{7}$ exhibits unique electronic and magnetic properties, such as giant magnetoresistance, a quasi-2D metallic ground state, and antiferromagnetic (AFM) order comprising of ferromagnetic bilayers coupled antiferromagnetically along the c-axis [1-3]. In this talk, we will show that only a few percent of Ti-doping at Ru sites can tune the ground state to a Mott-insulating state with ``G''-type, nearest neighbor AFM order [4]. We have established the electronic and magnetic phase diagram of this doped system to address the underlying physics of such a Mott-transition. We find that a strong scattering effect due to the Ti ions'' empty 3d orbital significantly reduces electrons'' itinerancy, playing a pivotal role in the suppression of the bilayer ferromagnetism and inducing the Mott transition. These findings imply that Ca$_{3}$Ru$_{2}$O$_{7}$ involves competition between the antiferromagnetism due to the Mott transition and the itinerant ferromagnetism due to a Stoner instability. [1] X.N. Lin et al., Phys. Rev. Lett. 95, 017203(2005). [2] W. Bao et al., Phys. Rev. Lett. 100, 247203 (2008). [3] Y. Yoshida et al., Phys. Rev. B 69, 220411 (R) (2004). [4] X. Ke et al., Phys. Rev. B 84, 201102 (R) (2011).