Nb-substitution effects in half-metallic double perovskite Ba2FeMoO6

We studied the structural, transport and magnetic properties in a half-metallic double perovskite Ba2FeMo1-xNbxO6 with 0 <= x <= 1. The observed systematic evolution of the non-metallic upturn with x in the resistivity suggests that the substitution of Nb5+ (4d(0)) for Mo5+ (4d(1)) diminishes the spin-polarized carriers. In addition, we observed a linear decrease of the Curie temperature T-C with x. It seems that T-C continuously reaches 0 K at x = 1.0, where the end material is a paramagnet with antiferromagnetic spin correlations. These results clearly indicate that the decrease of carrier electrons with the substitution gradually destroys the ferromagnetism. Ba2FeMo1-xNbxO6 is possibly a promising material to determine the mechanism of ferromagnetism in the double perovskites.