Distinction between two types of charge-ordered states in the rare earth manganates, Ln(0.5)A(0.5)MnO(3), based on chemical melting

摘要

Effects of cation substitution in the manganese site of charge-ordered (CO) rare earth manganates have been studied to find out how the properties 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 converted into a ferromagnetic metallic state by Cr3+ substitution. Chemical conversion of the charge-ordered state in the insulating manganates 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 ferromagnetic metal from 250 K (similar to T-c) down to low temperatures, without the intervening CO state as in the parent manganate. (C) 1998 Academic Press. [References: 13]