MAGNETIC AND ELECTRICAL PROPERTIES OF BI1-XSRXMNO3 - HOLE-DOPING EFFECT ON FERROMAGNETIC PEROVSKITE BIMNO3

摘要

Although La3+ and Bi3+ ions have similar ionic radii, the Bi1-xSrxMnO3 system was found to show quite different behavior from La1-xSrxMnO3 in which ferromagnetism with metallic conductivity is achieved by the ''double exchange mechanism.'' BiMnO3 which was synthesized under high pressure is a ferromagnetic insulator with T-c=105 K, in contrast to antiferromagnetic LaMnO3. Though Sr substitution in BiMnO3 increased conductivity, no metallic state was achieved up to the solid solution limit of x=0.67. Furthermore the saturation magnetic moment of 3.6 mu(B) observed in BiMnO3 decreased very rapidly with increasing x, and ferromagnetism disappeared for x>0.4. These observations suggest that the highly polarizable Bi3+ ion with 6s(2) lone pair would cause local distortion of the perovskite lattice, which presumably reduces the mobility of carriers. The origin of ferromagnetism in BiMnO3 requires a mechanism other than the double exchange theory. (C) 1997 Academic Press. [References: 22]