Distinction between Two Types of Charge-Ordered States in the Rare Earth Manganates,Ln0.5A0.5MnO3, Based on Chemical Melting

Abstract

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 theAsite cations, 〈rA〉, and the substituent cation. The insulating CO state ofLn0.5Ca0.5MnO3(Ln=Nd, Gd, or Y) is unaffected by substitution with Al3+and Fe3+, but the CO state in the Nd compound (〈rA〉=1.17 Å) 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 〈rA〉≥1.17 Å. Progressive substitution of Mn3+in Nd0.5Sr0.5MnO3(〈rA〉=1.24 Å) with Al3+and Fe3+renders the material an insulator. Substitution with Cr3+, however, makes it a ferromagnetic metal from 250 K (∼TC) down to low temperatures, without the intervening CO state as in the parent manganate.