No abstract

No abstract

In the quest of materials with high temperature ferromagnetism and low temperature anti-ferromagnetism, we prepare Co3-xMnxTeO6; (0 < x ≤ 2) solid solutions. Room temperature structural investigations on these solid solutions as a function of Mn concentration using Synchrotron X-ray diffraction (SXRD) and X-ray absorption near edge structure measurements in corroboration with magnetism are presented. Phase diagram obtained from Rietveld Refinement on SXRD data as a function of Mn concentration indicates doping disproportionate mixing of both monoclinic (C2/c) and rhombohedral (R 3¯) structure for x < 0.5, while only R 3¯ structure for x ≥ 0.5. Further, it shows increase in both lattice parameters as well as average transition metal-oxygen (Co/Mn-O) bond lengths for x ≥ 0.5. Co and Mn K-edge XANES spectra reveal that both Co and Mn are in mixed oxidation state, Co2+/Mn2+ and Co3+/Mn3+. Relative ratios of Co3+/Co2+ and Mn3+/Mn2+ obtained using Linear combination fit decrease with increasing x (for x ≥ 0.5). These structural and spectroscopic evidences are used to provide possible interpretation of the observed paramagnetic to ferromagnetic transition at around 185 K followed by an enhanced antiferromagnetic transition ∼45 K for x = 0.5.

We report structural, magnetic, and dielectric properties of oxygen deficient hexagonal BaFeO3−δ. A large dielectric permittivity comparable to that of other semiconducting oxides is observed in BaFeO3−δ. Magnetization measurements indicate magnetic inhomogeneity and the system shows a paramagnetic to antiferromagnetic transition at ∼160 K. Remarkably, the temperature, at which paramagnetic to antiferromagnetic transition occurs, around this temperature, a huge drop in the dissipation factor takes place and resistivity shoots up; this indicates the possible correlation among magnetic and dielectric properties. First principle simulations reveal that some of these behaviors may be explained in terms of many body electron correlation effect in the presence of oxygen vacancy present in BaFeO3−δ indicating its importance in both fundamental science as well as in applications.

The highly intense synchrotron-radiation-based X-ray beams offer an undisputed advantage in assessing the structural parameters of crystalline solids. Herein, through extensive synchrotron-based probing, an attempt was made to understand the structural attributes that dictate the variation of upconversion luminescence intensity (UCL) resulting from the distortion of local crystal field symmetry. Four different sets of UC crystals (NaYF 4 /Yb 3+ /Ln 3+ : Ln = Ho, Er, Tm) have been designed with varying Li + concentrations. The analysis indicated that, out of many possible structural factors, the compressive lattice strains generated in those systems exhibited an unexpected correlation with the respective UCL intensities near their maximum values, irrespective of the activator species. Interestingly, the single-activatorbased samples showed maximum UCL intensities when their respective compressive lattice strains reached close to a particular value. Through experimental evidence, these findings tend to extend and complement the existing hypothesis of symmetry distortion of a UC lattice by chemical manipulation.