The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples 1.INTRODUCTIONOver the last two years much progress has been made in establishing superconductivity unambiguously in MFe 2 As 2 (M=Ba,Sr,Ca,Eu) systems [1][2][3][4][5][6]. The pristine sample that has a Spin Density Wave (SDW) ground state is nudged into a superconducting (SC) state by electron/ hole doping and application of pressure [2,7,8,9,10]. Band structure calculations point to the fact that SDW state arises on account of the special 2D geometry of Fermi surface that is unstable to nesting [11,12]. Also associated with or preceding the magnetic transition is a tetragonal to orthorhombic structural transition, which is suppressed in the superconducting state. The strong interplay of structure, magnetism and electronic structure have been investigated recently in the Co substituted BaFe 2-x Co x As 2 system [13].The temperature composition phase diagrams determined for the different chemical substitutions at different sites in BaFe 2 As 2 [14,15,16] show a generic behaviour as a function of the concentration of the substituent, viz., a systematic suppression of the SDW transition, followed by co-existence of SDW and SC and the occurrence of a superconducting dome. Several transition metal (TM) substitutions with electrons in excess of Fe forming, BaFe 2-x TM x As 2 have been studied but the maximum T C has remained at ~25 K [17]. A much higher T C of 38 K and ~35 K, were however observed by optimal hole doping in the Ba 1-x K x Fe 2 As 2 [2] system and in BaFe 2 As 2 by application of high pressure [10]. A systematic investigation on the role of hydrostaticity, in the pressure dependent resistivity study of BaFe 2 As 2 , has revealed that uniaxial pressure favours the occurrence of high T C at 36 K whereas a lower T C of 29 K occurs under truly hydrostatic pressure [18]. Consistent with this finding are results that indicate that strained crystals of BaFe 2 As 2 and SrFe 2 As 2 display superconductivity at ambient pressure [19]. A compilation of structural data from several compounds of the related ReOFeAs (Re=rare-earth) superconducting family, indicates that T C is optimized at a particular Fe-As distance [20] and/or at a particular Fe-As tetrahedral angle [21], indicating that the local structure of the FeAs 4 tetrahedra plays a crucial role in determining T C . Devising schemes to effect structural distortions by chemical substitution that would lead to higher T C in the BaFe 2 As 2 system will be useful.Thus motivated, we examine the effect of Ru substitution at the Fe site in BaFe 2 As 2 . At the outset, it is clear that Ru is isoelectronic to Fe and being larger in size should 3 introduce steric effects, affecting the Fe-As bond length leading to distortions of the FeAs 4 tetrahedral motifs. In addition, the larger radius of the 4d electron shell should increase the metal-metal overlap in the Fe/Ru layer and increase the hybridization of metal atom with As leading to significant alterations in the electr...

High coercivity (9.47 kOe) has been obtained for oleic acid capped chemically synthesized CoFe(2)O(4) nanoparticles of crystallite size approximately 20 nm. X-ray diffraction analysis confirms the formation of spinel phase in these nanoparticles. Thermal annealing at various temperatures increases the particle size and ultimately shows bulk like properties at particle size approximately 56 nm. The nature of bonding of oleic acid with CoFe(2)O(4) nanoparticles and amount of oleic acid in the sample is determined by Fourier transform infrared spectroscopy and thermogrvimetric analysis, respectively. The Raman analysis suggests that the samples are under strain due to capping molecules. Cation distribution in the sample is studied using Mossbauer spectroscopy. Oleic acid concentration dependent studies show that the amount of capping molecules plays an important role in achieving such a high coercivity. On the basis of above observations, it has been proposed that very high coercivity (9.47 kOe) is the result of the magnetic anisotropy, strain, and disorder of the surface spins developed by covalently bonded oleic acid to the surface of CoFe(2)O(4) nanoparticles.

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Structural, dielectric, ferroelectric (FE), 119Sn Mössbauer, and specific heat measurements of polycrystalline BaTi1–xSnxO3 (x = 0% to 15%) ceramics are reported. Phase purity and homogeneous phase formation with Sn doping is confirmed from x-ray diffraction and 119Sn Mössbauer measurements. With Sn doping, the microstructure is found to change significantly. Better ferroelectric properties at room temperature, i.e., increased remnant polarization (38% more) and very low field switchability (225% less) are observed for x = 5% sample as compared to other samples and the results are explained in terms of grain size effects. With Sn doping, merging of all the phase transitions into a single one is observed for x ≥ 10% and for x = 5%, the tetragonal to orthorhombic transition temperature is found close to room temperature. As a consequence better electro-caloric effects are observed for x = 5% sample and therefore is expected to satisfy the requirements for non-toxic, low energy (field) and room temperature based applications.

Particle and energy transport in the tokamak edge transport barrier is analyzed in the presence of magnetic field perturbations from external resonant coils. In recent experiments such coils have been verified as an effective tool for mitigation of the edge-localized modes of type I. The observed reduction of the density in plasmas of low collisionality is explained by the generation of charged particle flows along perturbed field lines. The increase of the electron and ion temperatures in the barrier is interpreted by the reduction of perpendicular neoclassical transport with decreasing density and nonlocality of parallel heat transport. The found modification of the pressure gradient implies the stabilization of ballooning-peeling MHD modes responsible for type I ELMs.

It is shown that Ca2+ doping at Bi-site results in the release of weak ferromagnetism in BiFeO3. Structural transformation from rhombohedral to triclinic is observed with 10% Ca doping. Raman measurements show the presence of oxygen vacancies with Ca doping and no evidence of either intermediate valence or the tetravalence of iron is observed from Mössbauer measurements. No significant change in Neel temperature is observed with Ca doping. The observed weak ferromagnetism and ferroelectric nature at room temperature indicates the multiferroic nature of Bi1−xCaxFeO3 (x=5% and 10%) samples.