Spin polarized states in bismuth based manganites

Abstract

Transport properties of crystalline (La,Bi)1-xSr xMnO3 and Bi1/2Ca1/2MnO3 were studied in the spin-polarized states induced by chemical substitution or applied magnetic fields. Substitution of lanthanum for bismuth changes the ground state from antiferromagnetic insulator to ferromagnetic metal. The electronic states in the boundary region remain unclear due to the non-uniform distribution of lanthanum ions. Application of high magnetic fields to Bi 1-x(Sr,Ca)xMnO3causes negative magnetoresistance effects in the charge-ordered state. All the samples studied do not show metallic conduction even in the highly spin-polarized state. The nature of the spin-polarized insulating state is discussed in relation to the ferromagnetic insulators in lightly-doped manganites. © 2006 IOP Publishing Ltd.