Synthesis of new double perovskites La1.98Mn1.11Mo0.89O5.93 and La1.92Mn1.29Mo0.71O5.84: Characterization of structural and magnetic properties

Abstract

The synthesis, structural and magnetic characterization of two new perovskites La1.98Mn1.11Mo0.89O5.93 and La1.92Mn1.29Mo0.71O5.84 are reported. Combined Rietveld refinements of X-ray and neutron powder diffraction data indicate that both samples are monoclinic perovskites with space group P21/n. The distribution of the transition metals over the octahedral sites is highly ordered: Mn preferentially occupies 2c sites, while Mo mostly occupies 2d sites. Mn oxidation states were determined by means of high resolution Kβ Emission Spectroscopy. The susceptibility as a function of temperature measurements and hysteresis loops show complex magnetic behaviour of both perovskites. The refined magnetic cells indicate that La1.98Mn1.11Mo0.89O5.93 is ferrimagnetic as a result of the antiferromagnetic coupling of two ferromagnetic sub-lattices associated to 2d and 2c sites, while La1.92Mn1.29Mo0.71O5.84 is ferromagnetic due to ferromagnetic alignment of the two sub-lattices. The magnetic overall behaviour of the latter perovskite is interpreted in terms of delocalization of magnetic moments arising from ferromagnetic double-exchange interactions between Mn2+ and Mn3+.