We report α-Cu2V2O7 to be an improper multiferroic with the simultaneous development of electric polarization and magnetization below TC = 35 K. The observed spontaneous polarization of magnitude 0.55 µCcm −2 is highest among the copper based improper multiferroic materials. Our study demonstrates sizable amount of magneto-electric coupling below TC even with a low magnetic field. The theoretical calculations based on density functional theory (DFT) indicate magnetism in α-Cu2V2O7 is a consequence of ferro-orbital ordering driven by polar lattice distortion due to the unique pyramidal (CuO5) environment of Cu. The spin orbit coupling (SOC) further stabilize orbital ordering and is crucial for magnetism. The calculations indicate that the origin of the giant ferroelectric polarization is primarily due to the symmetric exchange-striction mechanism and is corroborated by temperature dependent X-ray studies.PACS numbers: 75.85.+t, 71.20.-b Recently multiferroic materials with mutually coupled ferroelectric (FE) and magnetic orders have attracted considerable interest for their versatile technological as well as fundamental importance. [1-4] A strong magneto-electric (ME) coupling is expected in improper magnetic mutiferroics where ferroelectricity is induced by a specific magnetic order. In the last one decade, several magnetic multiferroics have been discovered [5][6][7][8][9][10] where FE polarization is either associated with spiral magnetic structure induced by spin-orbit coupling (SOC) [11,12] or by symmetric exchange striction (SES) mechanism in case of collinear magnets. [7,13] Due to the secondary nature of the electric order, the value of the FE polarization in such magnetic multiferroics is much smaller (generally ∼ 0.01 µC.cm −2 ) compared to the 'proper' FE.[4] A recent breakthrough in this direction is the discovery of giant ferroelectricity (∼ 0.3 µC.cm −2 ) and large ME coupling in mixed valent manganate CaMn 7 O 12 below about 90 K [14] mediated by both Dzyaloshinski-Moriya (DM) interaction as well as exchange striction mechanism. [15] In this respect cuprates may be an attractive option as the orbital degrees of freedom and strong Coulomb correlations present in cuprates may not only lead to lattice distortion and magnetism but also possibly induce a coupling between them which are essential ingredients for multiferroicity.In view of the above, we investigated the Cu-based oxide Cu 2 V 2 O 7 in its orthorhombic α phase. Cu 2 V 2 O 7 crystallizes in at least three different polymorphs, namely α, β and γ-phases where only the α phase is noncentrosymmetric [16][17][18] and is important in the present context. It consists of magnetic Cu 2+ (3d 9 , S = 1 2 ) and nonmagnetic V 5+ (3d 0 , S = 0) metal ions making it a system having both partially filled and empty d shells similar to BiFeO 3 , BiMnO 3 , Pb(Fe 2/3 W 1/3 )O 3 etc. [19,20]. All Cu2+ ions are equivalent with fivefold coordination to oxygen atoms forming a distorted [CuO 5 ] polyhedron. Each Cu-polyhedron is linked with another two via edge s...

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Graphite oxide nanoplatelets (GOnP) were prepared using standard method and used to make GOnP‐polyvinyl alcohol (PVA) composites by using solution cast technique. Significant enhancement of electrical conductivity and dielectric permittivity of the GOnP/PVA composites are observed at low GOnP concentration (fGOnP = fc∼0.41 vol%) which is the percolation threshold value estimated from the concentration dependent transport and dielectric data. Nearly 300 times increase in dielectric permittivity (compared with that of PVA) is observed in the GOnP/PVA composite around fc. We notice interesting metal‐insulator like transition (a sudden increase in resistivity) from the temperature dependent resistivity data in the pure GOnP sample around TMI ∼ 275 K which is shifted to 300 K in the GOnP/PVA composite for fc = 0.41 vol%, indicating drastic change of sp3/sp2 ratio around respective TMI. The present graphite‐based composite material might be processed for different applications. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

The search of novel quasi‐1D materials is one of the important aspects in the field of material science. Toroidal moment, the order parameter of ferrotoroidic order, can be generated by a head‐to‐tail configuration of magnetic moment. It has been theoretically proposed that 1D dimerized and antiferromagnetic (AFM)‐like spin chain hosts ferrotoroidicity and has the toroidal moment composed of only two antiparallel spins. Here, the authors report a ferrotoroidic candidate of Ba6Cr2S10 with such a theoretical model of spin chain. The structure consists of unique dimerized face‐sharing CrS6 octahedral chains along the c axis. An AFM‐like ordering at ≈10 K breaks both space‐ and time‐reversal symmetries and the magnetic point group of mm′2′allows three ferroic orders in Ba6Cr2S10: (anti)ferromagnetic, ferroelectric, and ferrotoroidic orders. Their investigation reveals that Ba6Cr2S10 is a rare ferrotoroid ic candidate with quasi 1D spin chain, which can be considered as a starting point for the further exploration of the physics and applications of ferrotoroidicity.

A novel two-phase polymer nanocomposite film comprising of polyvinylidene fluoride (PVDF) and nanocrystalline ($90 nm) semiconducting multiferroic BiFeO 3 (BFO) have been fabricated by hot-molding technique. Such flexible thick nanocomposite films, semicrystalline in nature, exhibited extraordinarily high effective dielectric permittivity e eff $ 10 3 (compared with that of pure PVDF) near the low percolation threshold (f c ¼ 0.12) at room temperature (RT) and the films also possessed low dielectric loss ($0.18). The polarizationelectric field (P-E) hysteresis loops are displayed at RT, which indicate ferroelectric like behavior of PVDF still persists in the percolative nanocomposite. There is also large increase of remanent polarization of BFO in the composite indicating improvement of the multiferroic behavior of BFO embedded in the PVDF polymer. The sample also indicates good fatigue endurance. Formation of microcapacitors and percolative behavior are correlated to explain the obtained results based on the special geometry of the BFO nanofillers. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 572-579, 2012