We report a synthesis method to stabilize TiO2 rutile nanoparticles (around 10 nm) and keep the particle size when reduced down TiO1.84. TiO2−δ exhibit room-temperature ferromagnetism that becomes stronger for The reduction mechanism Magneli phases excludes relevant influence of oxygen vacancies in modification magnetic properties. arrangement Ti3+ could give rise hopping single 3d electron inducing local ferromagnetic-like behavior.

The evolution of the structure, magnetic ordering, and superconductivity in series Ba1−xNaxFe2As2 is reported up to limiting Na-rich composition with x = 0.6; more compositions are unstable at high temperatures respect competing phases. superconducting behaviors members similar those better-investigated Ba1−xKxFe2As2 analogues. This evidently a consequence quantitatively structure FeAs layers two series. In antiferromagnetic order an associated structural distortion evident for ≤ 0.35 when...

The synthesis and evolution of the structure, magnetic ordering, superconductivity layered iron arsenides Sr1-xNaxFe2As2 is reported. In solid solution, limiting Na-rich composition in samples made using conventional state at elevated temperatures occurs an unusually small value (x = 0.4) compared with other alkali-metal-doped alkaline earth arsenides. Above this sodium content, competing phases are formed: for x 0.42, elemental impurity evident, additional impurities appear > 0.42....

In this paper, the physical properties of half-doped manganite La0.5Ca0.5MnO3 with crystallite sizes ranging from 15 to 40 nm are investigated. As expected, ferromagnetic order strengthens at expense antiferromagnetic one as size is reduced nm. However, contrary previously reported works, an enhancement saturation magnetization observed increases 22 This unexpected behavior accompanied by unusual cell volume variation that seems induce ferromagnetic-like one. Besides, field cooled hysteresis...

A BaFeO3−δ (δ ≈ 0.22) perovskite was prepared by a sol–gel method and essayed as catalyst in the CO oxidation reaction. (0.22 ≤ δ 0.42) depicts 6H hexagonal structural type with Fe both III IV states oxygen stoichiometry accommodated random distribution of anionic vacancies. The highest content, BaFeO2.78, proved to be more active than its lanthanide-based counterparts, LnFeO3 (Ln = La, Sm, Nd). Removal lattice detected temperature-programmed (TPO) reduction (TPR) experiments at around 500 K...

Magnetoresistance (MR) in half doped copper LaCu0.5Mn0.5O3 manganese related perovskite, synthesized by means of a soft chemistry pathway, is reported. Characterization Rietveld refinement from powder X-ray diffraction data, SAED, HREM, and EELS indicates random occupation Cu2+ Mn4+ at the octahedral sites an orthorhombic perovskite lattice. This disordered situation agreement to absence charge ordering. exhibits antiferromagnetic behavior Mn4+–O–Mn4+ Cu2+–O–Cu2+ interactions. Ferromagnetic...

Electron diffraction and high-resolution electron microscopy of LaMnO3-δ (0 ≤ δ 0.25), obtained by topotactic reduction LaMnO3, shows that an ordered pathway anionic vacancies is only for = 0.25. La4Mn4O11 eightfold superlattice the perovskite-type structure due to intergrowth three octahedral layers one tetrahedral layer along b axis, according sequence ...OOOTOOOT'... The reduced sample exhibits ferromagnetic behavior with Tc ≈ 50 K. staircase effect, observed at low temperature, discussed...

Stair-like metamagnetic transitions in the oxygen deficient La0.5Ca0.5MnO3−δ perovskite are here for first time reported. This experimental fact sheds light on knowledge of transition anion phase segregations systems. Actually, it is shown that controlled reduction content constitutes an alternative pathway to chemical doping at A and B positions sublattice. In this way, point defects created inducing stair-like a CE-type AFM (antiferromagnetic) manganite.

The topotactic reduction of La0.5Sr0.5MnO3 leads to ordering the anionic vacancies in La0.5Sr0.5MnO2.5 composition. isolated material, which is isostructural with Sr2Fe2O5, crystallises brownmillerite structural type 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 electron diffraction high-resolution microscopy suggests a complex microstructure arising from coherent intergrowth different brownmillerite-type...

Abstract Thermogravimetry, X‐ray and electron diffraction high resolution microscopy show that the reduction process from perovskite La 0.5 Ca MnO 3 to brownmilleriteLa 2.5 is a reversible topotactic process. Two series of monophasic 3– δ oxygen‐deficient perovskites were stabilized in 0 ≤ 0.12 range, either or oxidation . Soft absorption spectroscopy shows Mn states differ as function synthetic pathway. Temperature dependence magnetization anionic vacancies concentration at constant doping...

Abstract Neutron diffraction and X‐ray absorption near‐edge structure (XANES) studies have been performed in La 0.5 Ca MnO 2.5 , Sr Nd oxygen‐deficient perovskite compounds obtained by topotactic reduction. They all exhibit a brownmillerite with G‐type antiferromagnetic ordering. Mn 2+ 3+ 4+ coexist at the octahedral sites, whereas only is placed tetrahedral positions. A magnetic moment of 1.6 μ B has detected layers, which can be explained assuming low‐spin configuration.

Magnetoimpedance spectroscopy was carried out on phase-separated La0.5Ca0.5MnO3 polycrystalline manganites. The powder synthesized following an adapted sol-gel route. Structural and magnetic data showed the signs of phase coexistence ferromagnetic (FM) Pnma charge-ordered antiferromagnetic (CO-AFM) P21/m phases. Magnetization vs. temperature (M T) measurements revealed several transitions from high paramagnetic (PM) to FM upon cooling (PM-FM) at ≈240 K, FM-AFM (≈170 K) AFM-FM (≈100 K)....

Ruddlesden–Popper's manganates, An+1MnnO3n+1, built from the ordered intergrowth between one rock-salt and n perovskite blocks, display a wide variety of functionalities related to their physical-chemistry properties which can be in principle tuned by chemical modifications. Nevertheless, poor thermodynamic stability high members constitutes an inherent impediment, limiting development new this family. Actually, for ≥ 2, defects involving disordered intergrowths blocks are always present...

Oxygen engineering is an important tool for on-demand tailoring of manganese related perovskites into optimized performances.Anionic vacancies can be induced in both doped and undoped manganites by means topotactic reduction processes under oxygen controlled atmosphere.This has given rise to the stabilization new phases as a consequence ordering which Mn 2+ appears due reducing process.Different pathways are proposed LaMnO 3 systems.FM interactions remain at octahedral layers when longrange...

Non-stoichimetric LaMnO 3+ δ nanoparticles have been prepared and characterized. 3 changes the ground state from AFM to FM when particle size is reduced. La 0.93 Mn O shows a noticeable magnetoresistance effect.

Abstract Resistance measurements indicate the presence of magnetoresistance in La 0.5 Sr MnO 2.5 brownmillerite related compound. An 80 % is found at 75 K. In spite partial break‐up occurring 3D network octahedra sharing corners, characteristic full oxygen content perovskite phase, deficient compound exhibits complex magnetic and electric properties. Such behavior can be explained on basis ferromagnetic metallic clusters randomly distributed octahedral layers separated from each other by an...

While being key to understanding their intriguing physical properties, the origin of nanophase separation in manganites and other strongly correlated materials is still unclear. Here, experimental evidence offered for controverted phase mechanism representative La1-xCaxMnO3 system. For low hole densities, direct Mn(4+) holes localization around Ca(2+) ions experimentally provided by means aberration-corrected scanning transmission electron microscopy combined with energy loss spectroscopy....

On the basis of magnetization and resistivity measurements in La1-xCaxMnO3 system, a model is proposed for explaining complex magnetic magnetoresistant behavior along 0.80 < x 1 composition range. This assumes localization Mn3+ cations around La3+ substitutional atoms resulting ferromagnetic nanoclusters, about 0.9 nm size, due to double exchange interactions with Mn4+ surrounding being responsible behavior. The allows one explain both hole electron doping regions system.

Abstract A reversible topotactic oxidizing–reducing process has been clearly evidenced in the annealing treatment followed to stabilize rhombohedral and orthorhombic La 1– t Mn O 3 (0.016 ≤ 0.038) samples. The study of surface evolution by characterization scanning electron microscopy (SEM) atomic force (AFM) gives evidence for a diffusion mechanism cations through grain boundaries which provides fast pathway perovskite related compound; however, contrary theoretical predictions, overall...

We describe here a type of magnetoresistance that takes place in naturally layered and outstanding ordered single phase manganites may be mediated by magnon excitation. In particular, we show the effect for Ruddlesden-Popper compound, $\mathrm{LaS}{\mathrm{r}}_{2}\mathrm{M}{\mathrm{n}}_{2}{\mathrm{O}}_{7}$ synthesized ceramic method. This material exhibits, besides conventional colossal magnetoresistance, another at low temperature, associated with breaking A-type antiferromagnetic coupling...

Data are presented on the thermal dependence of hysteretic properties cationic vacancies including manganite samples composition LaMnO3+δ (δ=0.05 and 0.12). Our results evidence presence in both two magnetic phases having ferro- antiferromagnetic orders, respectively. The temperature coercivity relaxational is closely linked to connectivity moment bearing Mn3+–Mn4+ ferromagnetic clusters that demagnetize independently case δ=0.05 sample collectively δ=0.12 one, as evidenced from activation...

The inclusion of La-Mn vacancies in LaMnO3 nanoparticles leads to a noticeable change conductivity behavior. sample retains its overall insulator characteristic, with typical thermal activation mechanism at high temperatures, but it presents magnetoconductivity below 200 K. energy decreases linearly the square reduced magnetization and vanishes when is magnetized saturation. Therefore, turns out that electron hopping between Mn3+ Mn4+ largely contributes Curie temperature. influence applied...