DISTINCTION BETWEEN 2 TYPES OF CHARGE-ORDERED STATES IN THE RARE-EARTH MANGANATES, LN(0.5)A(0.5)MNO(3), BASED ON CHEMICAL MELTING

Effects of cation substitution in the manganese site of charge-ordered (CO) rare earth manganates have been studied to find out how the prop erties vary with the average radius of the A site cations, (r(A)), and the substituent cation, The insulating CO state of Ln(0.5)Ca(0.5)MnO( 3) (Ln = Nd, Gd, or Y) is unaffected by substitution with Al3+ and Fe3 +, but the CO state in the Nd compound ([r(A)] = 1.17 Angstrom) is con verted into a ferromagnetic metallic state by Cr3+ substitution. Chemi cal conversion of the charge-ordered state in the insulating manganate s by Cr3+ substitution seems to occur only when (r(A)) greater than or equal to 1.17 Angstrom. Progressive substitution of Mn3+ in Nd0.5Sr0. 5MnO3 ([r(A)] = 1.24 Angstrom) with Al3+ and Fe3+ renders the material an insulator. Substitution with Cr3+, however, makes it a ferromagnet ic metal from 250 K (similar to T-c) down to low temperatures, without the intervening CO state as in the parent manganate. (C) 1998 Academi c Press.