Very recent report 1 on observation of superconductivity in Bi 4 O 4 S 3 could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here synthesis of Bi 4 O 4 S 3 at 500 0 C by vacuum encapsulation technique and its basic characterizations. Bi 4 O 4 S 3 is contaminated by small amounts of Bi 2 S 3 and Bi impurities. The majority phase is tetragonal I4/mmm space group with lattice parameters a = 3.9697(2)Å, c = 41.3520(1)Å. Both AC and DC magnetization measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (T c ) of 4.4K. Isothermal magnetization (MH) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H c1 ) at 2K, of the new superconductor is found to be ~15 Oe. The magneto-transport R(T, H) measurements showed a resistive broadening and decrease in T c (ρ=0) to lower temperatures with increasing magnetic field. The extrapolated upper critical field H c2 (0) is ~ 31kOe with a corresponding Ginzburg-Landau coherence length of ~100Å . In the normal state the ρ ~ T 2 is not indicated. Hall resistivity data show non-linear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 . On the other hand same temperature heat treated Bi is not superconducting, thus excluding possibility of impurity driven superconductivity in the newly discovered Bi 4 O 4 S 3 superconductor.

We report multiferroic behavior in double perovskite Y 2 CoMnO 6 with ferroelectric transition temperature T c = 80K. The origin of ferroelectricity is associated with magnetic ordering of Co 2+ and Mn 4+ moments in a ↑↑-↓↓ arrangement. The saturation polarization and magnetization are estimated to be 65 µC/m 2 and 6.2 µ B /f.u. respectively. The magnetoelectric coupling parameter, on the other hand, is small as a 5 Tesla field suppresses the electric polarization by only ~8%. This is corroborated with observed hysteretic behaviour at 5K that remains unsaturated even upto 7 Tesla. A model based on exchange-striction is proposed to explain the observed high temperature ferroelectricity. a) spatnaik@mail.jnu.ac.in

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We report observation of magneto-electric and magneto-dielectric couplings along with short range ferromagnetic order in ceramic Cobalt Tellurate (Co3TeO6, CTO) using magnetic, structural, dielectric, pyroelectric, and polarization studies. DC magnetization along with dielectric constant measurements indicate a coupling between magnetic order and electrical polarization. A strong anomaly in the dielectric constant at ∼17.4 K in zero magnetic field indicates spontaneous electric polarization, consistent with a recent neutron diffraction study. Observation of weak short range ferromagnetic order at lower temperatures is attributed to the Griffiths-like ferromagnetism. Furthermore, magnetic field dependence of the ferroelectric transition follows earlier theoretical predictions, applicable to single crystal CTO. Finally, combined dielectric, pyroelectric, and polarization measurements suggest that the ground state of CTO may possess spontaneous symmetry breaking in the absence of magnetic field.

Abstract:We report NdCrTiO 5 to be an unusual multiferroic material with large magnetic field dependent electric polarization. While magneto-electric coupling in this two magnetic sublattice oxide is well established, the purpose of this study is to look for spontaneous symmetry breaking at the magnetic transition. The conclusions are based on extensive magnetization, dielectric and polarization measurements around its antiferromagnetic ordering temperature of 18K. Room temperature X-ray diffraction pattern of NdCrTiO 5 reveals that the sample is single phase with an orthorhombic crystal structure that allows linear magneto-electric coupling. DC magnetization measurement shows magnetization downturn at 11K together with a small kink corresponding to the Co +3 sub-lattice ordering at~18K. An anomaly in dielectric constant is observed around the magnetic ordering temperature that increases substantially with increasing magnetic field. Through detailed pyroelectric current measurements at zero magnetic field, particularly as a function of thermal cycling, we establish that NdCrTiO 5 is a genuine multiferroic material that is possibly driven by collinear magneto-striction.Introduction: