An unusual magnetic structure in Sr2FeO3F and magnetic structures of K2NiF4-type iron(III) oxides and oxide halides, including the cobalt substituted series Sr2Fe 1-xCoxO3Cl

Journal article, 2005

An unusual k = [1/2 1/2 1/2] magnetic structure is reported in Sr 2FeO3F at low temperature. The magnetic structures of LaBaFeO4, LaSrFeO4, LaCaFeO4, Ca 2FeO3Cl, Ca2FeO3Br, Sr 2FeO3F, Sr2FeO3Cl, Sr 2FeO3Br and solid solutions in the series Sr 2Fe1-xCoxO3Cl have been examined and only Sr2FeO3F exhibits this structure. The La 2CuO4-type spin arrangement dominates in all these phases, with antiferromagnetic ordering in the xy planes. The k = [1/2 1/2 1/2] magnetic phase in Sr2FeO3F occurs below 100 K and requires La2CuO4-type stacking across the SrO layers and La2NiO4-type stacking across the SrF layers. It has been possible to show that this phase grows in domains which have purely La 2CuO4-type stacking at higher temperatures. In the Sr 2Fe1-xCoxO3Cl series the La 2CuO4-type magnetic structure in Sr2FeO 3Cl and the La2NiO4-type structure in Sr 2CoO3Cl coexist and structural and magnetic behaviour indicate phase segregation into cobalt- and iron-rich regions.