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Abstract: Polycrystalline and single crystalline samples of CaFe2As2 were prepared by using different fabrication routes. These samples show evident differences in both phase transition temperatures and transport properties depending on fabrication conditions. TEM observations reveal a rich variety of structural phenomena in these materials, such as a tweed-like pattern in self-flux samples, a structural modulation along the 〈110〉tetra direction in the polycrystalline sample, and complex dislocation networks in the Sn-flux samples. Careful analysis shows that the twinning domains arising from the tetragonal-to-orthorhombic phase transition belong to the δ-type. [Copyright &y& Elsevier]

Abstract: SrMn2As2 single crystals were grown by the Sn flux method. Structural features of these crystals were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that the single crystal has a rhombohedral structure and grows along the c-axis direction. The microstructure and layered structural features of this material have been examined by SEM and high-resolution TEM observations. The measurements of in-plane resistivity as a function of temperature demonstrate that SrMn2As2 undergoes a phase transition of semiconductor–insulator at a low temperature; the active energies are estimated to be Δ=0.64 and 0.29eV for two distinct regions. Magnetic measurements show a clear antiferromagnetic (AFM) transition at about T N =125K. Therefore, the SrMn2As2 material is an AFM insulator at low temperatures and could be a potential parent compound for superconductors. [Copyright &y& Elsevier]

Abstract: A new dual-phase nanocomposite magnet, made up of the well-coupled Sm3(Fe,Ti)29N x and α-Fe nano-crystals, has been successfully fabricated by the melt-spun technique. Measurements of magnetic properties reveal that the hysteresis loop shows up the notable characteristics of single hard magnet in the well-crystallized samples. The electron microscopy investigations indicate that the grain sizes in our samples in general range from 30 to 60nm for Sm3(Fe,Ti)29N x and from 10 to 20nm for α-Fe, grain boundaries between the Sm3(Fe,Ti)29N x and α-Fe phases are clean without any impurities. These structural features are fundamentally compatible with direct exchange-coupling between these two magnetic phases. [Copyright &y& Elsevier]

Structural distortions arising from the condensations of two essential kinds of phonon modes: the triply degenerate rotational modes (ϕx,ϕy,ϕz) of MnO6 and the doubly degenerate Jahn–Teller active modes (Q1,Q2) have been systematically investigated in the perovskite manganites. Microstructural features associated with certain types of distortions have been observed by transmission electron microscopy (TEM). In RMnO3 and La(Sr)2NiO4, we characterize the local structure, charge ordered states and orbital ordering by means of low-temperature TEM. We present direct evidence that the stripe modulation in La(Sr)2NiO4 is indeed one-dimensional within each NiO2 plane. Several typical kinds of defect structures, including antiphase boundaries and the 90°-twin domains, appear commonly in the charge-ordered states. [Copyright &y& Elsevier]