Electronic phase diagram in bandwidth controlled manganites

Electronic and magnetic properties for doped manganites, (i) R1/2Ca1/2Mn1-y CryO3 (y=0.03) and (ii) Na(1/2+delta)A(1/2-delta)MnO(3) (delta = 0.05), whe re R and A are the trivalent ran-earth and divalent alkaline-earth ions, re spectively, have been investigated by systematically changing the averaged ionic radius [r(A)] of perovskite A-site, or the one-electron bandwidth W. In the former system, the charge-ordered (CO) state is unstabilized by Cr-d oping on the Mn-site. On the other hand. deviation of doping-level from the quarter-filling (x = 1/2) weakens the CO state in the latter cast. We have derived electronic phase diagrams for both the systems against [r(A)]. We have found a phase separated region near the ferromagnetic metallic (FM)-CO phase boundary. (C) 2000 Elsevier Science B.V. All rights reserved.