Competition between Band Filling and Steric Effect in Ordered Double Perovskites Sr2 – x Lax MnMoO6

The ordered double perovskites, Sr2 – xLaMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2 – xLaxMnMoO6 (0 ≤ x ≤ 1). The compounds have a monoclinic structure (space group P21/n) and the cell volume expands monotonically with La doping. The Tc and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2 – xLaxMnMoO6 decreases only at low doping levels (x ≤ 0.2); while at high doping levels (0.8 ≤ x ≤ 1), electrical resistivity tends to increase greatly. The results suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.