Mn-site doped CaMnO3:: Creation of the CMR effect

The doping of CaMnO3-delta at Mn sites with pentavalent and hexavalent d(0) elements - Nb, Ta, W, Mo - modifies the resistivity behavior of this phase, extending the insulating domain and increasing significantly the resistivity at low temperature as the doping element content increases. The higher valency of the doping element introduces electrons; i.e., Mn3+ species are formed in the Mn4+ matrix. Double exchange phenomena then allow ferromagnetic interactions, by application of external magnetic fields which are similar to those observed for electron-doped manganites Ca(1-x)Ln(x)MnO(3) (x less than or equal to 0.15), but with smaller magnetic moments. Consequently, this Mn site doping induces CMR properties with resistivity ratios considerably larger than those for CaMnO3-delta. 2000 Academic Press.