The evolution of the structure, magnetic ordering, and superconductivity in the series Ba 1-x Na x-Fe 2 As 2 is reported up to the limiting Na-rich composition with x = 0.6; the more Na-rich compositions are unstable at high temperatures with respect to competing phases. The magnetic and superconducting behaviors of the Ba 1-x Na x Fe 2 As 2 members are similar to those of the betterinvestigated Ba 1-x K x Fe 2 As 2 analogues. This is evidently a consequence of the quantitatively similar evolution of the structure of the FeAs layers in the two series. In Ba 1-x Na x Fe 2 As 2 antiferromagnetic order and an associated structural distortion are evident for x e 0.35 and superconductivity is evident when x exceeds 0.2. For 0.4 e x e 0.6 bulk superconductivity is evident, and the long-range antiferromagnetically ordered state is completely suppressed. The maximum T c in the Ba 1-x Na x-Fe 2 As 2 series, as judged by the onset of diamagnetism, is 34 K in Ba 0.6 Na 0.4 Fe 2 As 2 . Despite the large mis-match in sizes between the two electropositive cations which separate the FeAs layers, there is no evidence for ordering of these cations on the length scale probed by electron diffraction.
The synthesis and evolution of the structure, magnetic ordering, and superconductivity of the layered iron arsenides Sr 1-x Na x Fe 2 As 2 is reported. In the Sr 1-x Na x Fe 2 As 2 solid solution, the limiting Na-rich composition in samples made using conventional solid state synthesis at elevated temperatures occurs at an unusually small value (x = 0.4) compared with other alkali-metal-doped alkaline earth iron arsenides. Above this limiting value of the sodium content, competing phases are formed: for x = 0.42, an elemental iron impurity is evident, and additional impurities appear for x>0.42. Superconductivity is detected in the compositions approaching the phase limit (T c = 26 K for x = 0.4) in line with analogous isoelectronic materials. However, the magnetically ordered state which competes with the superconducting state appears not to be completely suppressed even at the limiting composition. The Na doping of SrFe 2 As 2 is contrasted with the K-doping of SrFe 2 As 2 and Na-doping of BaFe 2 As 2 and other "122" iron arsenide compounds.
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.
We report a synthesis method to stabilize TiO 2 rutile nanoparticles (around 10 nm) and keep the particle size when reduced down to TiO 1.84 . TiO 2−δ nanoparticles exhibit room-temperature ferromagnetism that becomes stronger for TiO 1.84 . The reduction mechanism to stabilize Magneli phases excludes a relevant influence of oxygen vacancies in the modification of the magnetic properties. The arrangement of Ti 3+ could give rise to hopping of the single 3d electron inducing local ferromagnetic-like behavior.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.