Severe Fermi Surface Reconstruction at a Metamagnetic-Transition in   Ca$_{2-x}$Sr$_x$RuO$_4$ (for $0.2 \leq x \leq 0.5$)
  We report an electrical transport study in Ca$_{2-x}$Sr$_{x}$RuO$_4$ single crystals at high magnetic fields ($B$). For $x =0.2$, the Hall constant $R_{xy}$ decreases sharply at an anisotropic metamagnetic (MM) transition reaching its value for Sr$_2$RuO$_4$ at high fields. A sharp decrease in the $A$ coefficient of the resistivity $T^2$-term and a change in the structure of the angular magnetoresistance oscillations (AMRO) for $B$ rotating in the planes, confirms the reconstruction of the Fermi surface (FS). Our observations and LDA calculations indicate a strong dependence of the FS on the Ca concentration and suggest the coexistence of itinerant and localized electronic states in single layered ruthenates. 
L. Balicas, S. Nakatsuji, D. Hall, H. Lee, Z. Fisk, Y. Maeno, and D.   J. Singh