Interplay of superconductivity and antiferromagnetism in SmRh4B4

A microscopic theory of interplay of superconductivity and antiferromagnetism in rare earth ternary systems is developed from first principles for less than half filledf atomic shells. Self consistent equations for the superconducting order parameter Δ and magnetic order parameter Γ, are derived using a Green’s function technique and equation of motion method. The theory is applied to explain the experimental results in the antiferromagnetic superconductor SmRh₄B₄. The present model explains true coexistence of superconductivity and antiferromagnetism and the suppression of superconductivity by antiferromagnetism. The behaviour of superconducting order parameter (Δ), magnetic order parameter (Γ), the specific heat, the density of states, free energy and critical field (H _c) is also studied for the system SmRh₄B₄.     

Ag2CuMnO4: A new silver copper oxide with delafossite structure

The use of hydrothermal methods has allowed the synthesis of a new silver copper mixed oxide, Ag₂CuMnO₄, the first example of a quaternary oxide containing both elements. It crystallizes with the delafossite 3R structure, thus being the first delafossite to contain both Ag and Cu. Synthesis conditions affect the final particle size (30-500 nm). Powder X-ray diffraction Rietveld refinement indicates a trigonal structure and cell parameters and , where Cu and Mn are disordered within the octahedral B positions in the plane and linearly coordinated Ag occupies de A position between layers. X-ray absorption near edge spectroscopy (XANES) for copper and manganese, and XPS for silver evidence +2, +4, and +1 oxidation states. The microstructure consists of layered particles that may form large twins showing 5 nm nanodomains. Finally, magnetic measurements reveal the existence of ferromagnetic coupling yielding in-plane moments that align antiferromagnetically at lower temperatures. The singularity of the new phase resides on the fact that is an example of a bidimensional arrangement of silver and copper in an oxide that also shows clear bidimensionality in its physical properties. That is of special relevance to the field of high T_c superconducting oxides, while the ferromagnetic coupling in a bidimensional system deserves itself special attention.     

Magnetic properties of bridged azido complexes

It was shown on the basis of the generalized angular overlap model that specific features of the electronic structure of the N₃ ^– anion in polynuclear complexes with the M(_1,1-N_{3 2}M magnetic fragment should result in strong ferromagnetism. The _1,3-N₃ coordination mode favors antiferromagnetic properties. The theoretical results agree with experimental magnetostructural correlations.     

Strong magnetic interactions through weak bonding interactions in organometallic radicals: combined experimental and theoretical study

The magnetic properties of a series of three neutral radical organometallic complexes of general formula [CpNi(dithiolene)]. have been investigated by a combination of X-ray crystal structure analysis and magnetic susceptibility measurements, while the assignment of the exchange coupling constants to the possible exchange pathways has been accomplished with the help of calculations based on density functional theory (DFT). The syntheses and X-ray structures of [CpNi(adt)] (adt=acrylonitrile-2,3-dithiolate) and [CpNi(tfd)] (tfd=1,2-bis(trifluoromethyl)ethene-1,2-dithiolate) complexes are described, while [CpNi(mnt)] (mnt=maleonitriledithiolate) was reported earlier. In the three complexes, we observed strong antiferromagnetic coupling that could not be explained solely by short SS intermolecular contacts. Our calculations indicated that spin density in these complexes is strongly delocalized on the NiS2 moiety, with up to 20% on the Cp ring. As a consequence, CpCp and Cpdithiolene overlap interactions have been identified as responsible for antiferromagnetic couplings. The [CpNi(adt)] complex thus has a value J=-369.5 cm(-1) for an exchange interaction through a pi stacking due to the CpCp overlap.     

Study of dielectric properties of single phase Bi1−xCaxFeO3 (x = 0.1, 0.3, 0.5)

A series of Bi_1−xCa_xFeO₃ (x = 0.1, 0.3, 0.5) multiferroic samples have been prepared in order to study the effect of different concentrations of Ca on the crystal structure, and dielectric properties. Structural analysis has been performed using X-ray diffraction (XRD) measurements. Rietveld refined XRD data confirm that all the samples are of single phase, having hexagonal structure with R3c space group. Cell parameters decrease systematically with increase in Ca concentration. Dielectric measurements have been performed in the temperature range of 200–450 K at selected frequencies in the range 100–1100 kHz. A near room temperature ferroelectric anomaly has been observed in all the samples which shift toward lower temperature with increase in doping. Conduction activation energies are calculated and found to decrease with increasing doping.