We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe 2 As 2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at 49 K, which has a low critical field < 4 Oe, and the other at 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe 2 As 2 (or Ae122), where Ae = Ca, Sr, or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature ( T c ) only up to 38 K and pressurization has been reported to produce superconductivity with a T c up to 30 K. The unusual 49 K phase detected will be discussed.

The Raman spectra of single crystals of NiFe2O4 were studied in various scattering configurations in close comparison with the corresponding spectra of Ni0.7Zn0.3Fe2O4 and Fe3O4. The number of experimentally observed Raman modes exceeds significantly that expected for a normal spinel structure and the polarization properties of most of the Raman lines provide evidence for a microscopic symmetry lower than that given by the F d3m space group. We argue that the experimental results can be explained by considering the short range 1:1 ordering of Ni 2+ and Fe 3+ at the B-sites of inverse spinel structure, most probably of tetragonal P 4122/P 4322 symmetry.

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Millimeter size single crystals of double perovskite La2NiMnO6 (LNMO) were grown by the High Temperature Solution Growth Method. The magnetic measurements and polarized Raman spectra between 5 and 350 K provide evidence that the crystals have high degree of Ni 2+ /Mn 4+ ordering, small amount of lattice defects and highest Tc = 288 K reported so far for ferromagnetic double perovskites. At a microscopic level the crystals are heavily twinned and the effect of twinning on the Raman spectra is analyzed in detail.