Ferromagnetism in a New Manganese‐Related Brownmillerite: La_0.5Sr_0.5MnO_2.5

Abstract

The topotactic reduction of La0.5Sr0.5MnO3 leads to ordering of the anionic vacancies in the La0.5Sr0.5MnO2.5 composition. The isolated material, which is isostructural with Sr2Fe2O5, crystallises in the brownmillerite structural type with unit cell parameters a=0.54117(3), b=1.67608(12), c=0.54004(3) nm and space group Ibm2. Its microstructural characterisation by means of electron diffraction and high-resolution electron microscopy suggests a complex microstructure arising from the coherent intergrowth of different brownmillerite-type domains that show short-range ordering at the A sub-lattice. The layer structure of La0.5Sr0.5MnO2.5 leads to a double magnetic behaviour where a ferromagnetic two-dimensional component is present.

Revisiting the Role of Vacancies in Manganese Related Perovskites

“…12c). For La 0.5 Sr 0.5 MnO 2.5 the SAED and HREM studies confirm the brownmillerite cell [26]. It is, again, remarkable the presence of twinned domains in each crystal as reflected in the HREM image displayed in Fig.…”

“…In this case, this FM contribution cannot be related to the starting material. According to previous XANES data [19] and the rest of Mn 2+ occupies the octahedral ones is proposed [26]. However, the presence of Mn 3+ and Mn 4+ at the octahedral position is not enough to ensure the FM behaviour because it appears in La 0.5 Sr 0.5 MnO 2.5 but not in La 0.5 Ca 0.5 MnO 2.5 .…”

“…The aim of this work is to analyse in depth the reduction process of La 1-x AT x MnO 3 (AT=Ca, Sr) focussing, mainly, on chemical and structural concerns related to the reaction. In this sense, we will concentrate on LaMnO 3-(x=0) and La 0.5 Sr 0.5 MnO 3-(x=0.5) systems, in which we have recently reported the stabilization of LaMnO 2.75 [25] and La 0.5 Sr 0.5 MnO 2.5 [26], whereas the reaction pathway as well as the stabilization of other reduced phases has not been described in detail. Moreover, the Ln 0.5 AT 0.5 MnO 3-system admits compositional changes at the Ln and AT sublattice while the oxygen stoichiometry is kept constant and equal to 2.5.…”

“…Hansteen et al [24] have reported LaMnO 3-(0.08 <0.25) but mixtures of phases were obtained through a zircothermal reduction processes. More recently, LaMnO 2.75 ( =0.25) has been stabilized by topotactic reduction of LaMnO 3 in a thermobalance [25] hence showing that further oxygen reduction can be obtained if La is partially substituted by Ca [23] or Sr [26]. The aim of this work is to analyse in depth the reduction process of La 1-x AT x MnO 3 (AT=Ca, Sr) focussing, mainly, on chemical and structural concerns related to the reaction.…”

Long and Short Ordering in Cationic Deficient Manganese Related Brownmillerites

“…Although plenty of works has been devoted to the first point, less effort has been devoted to study the effect of the compositional variations at the oxygen sublattice. In spite of the partial breakup occurring at the 3D network of octahedral sharing corners, responsible of the double exchange interactions the oxygen deficient compounds exhibits complex magnetic and electric properties [1].In this context, we have recently shown the stabilization of a new brownmillerite (B) compound La 0.5 Sr 0.5 MnO 2.5 [2], built up of octahedral and tetrahedral layers sharing corners, exhibiting CMR. In this compound Mn 2+ , Mn 3+ and Mn 4+ oxidation states coexist leading to complex electric and magnetic behaviours.…”