Metal-Insulator Transition and Ferromagnetism in the Electron Doped   Layered Manganites La2.3-xYxCa0.7Mn2O7 (x=0,0.3,0.5)
  Bulk samples of La2.3-xYxCa0.7Mn2O7, x=0,0.3,0.5, with layered perovskite structure have been synthesized and investigated with respect to their electrical, electronic and magnetic properties. It is found that La1.8Y0.5Ca0.7Mn2O7 has tetragonal structure and is a metallic ferromagnet with a magnetic transition temperature of 170 K. The compound shows metallic behavior below 140 K and has a large magnetoresistance (MR) Delta-rho/rho(0)~94% at 100 K at 34 kOe. For x=0 and 0.3 the structure is monoclinic with a suppression of metallicity. For x=0 the material is an ferromagnetic insulator. We observed a large increase in the coefficient of the linear term in specific heat with decreasing x. As far as we are aware, this is the first report of an electron doped manganite showing metal-insulator transition and ferromagnetism. 
P. Raychaudhuri, C. Mitra, A. Paramekanti, R. Pinto, A. K. Nigam, S.   K. Dhar