Preparation, Crystal Structure, and Magnetic and Magnetotransport Properties of the Double Perovskite Ca₂FeMoO₆

Abstract

Ca2FeMoO6 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 P21/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 FeO6 and MoO6 octahedra, considerably tilted due to the relatively small size of the Ca2+ cations. Low-temperature (2 K) NPD data show evidence for a ferrimagnetic coupling between the Fe3+ and Mo5+ sublattices, with ordered magnetic moments of 3.2(1) and −0.76(6) μB, respectively. The Curie temperature is 380 K. Both magnetism and transport indicate a large component of itinerancy for down-spin Fe t2g 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 9T, significantly larger than that reported for other A2FeMoO6 perovskites, A = Sr, Ba.