Preparation, Crystal Structure, and Magnetic and Magnetotransport Properties of the Double Perovskite Ca 2 FeMoO 6

Ca 2 FeMoO 6 perovskite has been prepared in polycrystalline form by controlled reduction of previously decomposed citrate precursors. This material has been studied by X-ray and neutron powder diffraction (NPD), scanning electron microscopy, thermal analysis, and magnetic and magnetotransport measurements. The crystal structure is monoclinic, space group P 2 1 / n, with a = 5.4150(1), b = 5.5224(1), c = 7.7066(2) Å, and β = 89.969(8)° at room temperature (RT). The crystal contains alternating FeO 6 and MoO 6 octahedra, considerably tilted due to the relatively small size of the Ca 2+ cations. Low-temperature (2 K) NPD data show evidence for a ferrimagnetic coupling between the Fe 3+ and Mo 5+ sublattices, with ordered magnetic moments of 3.2(1) and −0.76(6) μ B, respectively. The Curie temperature is 380 K. Both magnetism and transport indicate a large component of itinerancy for down-spin Fe t 2g electrons. The carrier density measured by the Hall effect is 0.031 holes per formula unit at 100 K. A magnetoresistance of 30% has been observed at RT for 9 T, significantly larger than that reported for other A 2 FeMoO 6 perovskites, A = Sr, Ba.