We observe an enormous spontaneous exchange bias (~300-600 Oe)--measured in an unmagnetized state following zero-field cooling--in a nanocomposite of BiFeO(3) (~94%)-Bi(2)Fe(4)O(9) (~6%) over a temperature range 5-300 K. Depending on the path followed in tracing the hysteresis loop--positive (p) or negative (n)--as well as the maximum field applied, the exchange bias (H(E)) varies significantly with | - H(Ep) | > | H(En) |. The temperature dependence of H(E) is nonmonotonic. It increases, initially, till ~150 K and then decreases as the blocking temperature T(B) is approached. All these rich features appear to be originating from the spontaneous symmetry breaking and consequent onset of unidirectional anisotropy driven by "superinteraction bias coupling" between the ferromagnetic core of Bi(2)Fe(4)O(9) (of average size ~19 nm) and the canted antiferromagnetic structure of BiFeO(3) (of average size ~112 nm) via superspin glass moments at the shell.

Transparent poly(vinyl alcohol) (PVA) hydrogel films, derived from aqueous solutions of varying concentration, were synthesized by the cyclic freeze-thaw method (0°-37 °C). This study demonstrates a variation in the transparency, degree of crystallinity, wettability, swelling and mechanical properties of the hydrogels as a function of the solution concentration and the number of freeze-thaw cycles for a given average molecular weight (95,000 Da). The study manifests a strong control of the number of freeze-thaw cycles on the structure-property correlations of the synthesized transparent PVA hydrogels, revealing the possibility of obtaining a window of structural and process parameters for the physically cross-linked hydrogels, making them suitable for cell-gel interactions.

Introduction: Bacterial vaginosis is a polymicrobial syndrome involving replacement of normal vaginal hydrogen peroxide producing lactobacilli by a variety of mycoplasmas and Gram-negative rods. Bacterial vaginosis has been conventionally diagnosed using Amsel criteria (a clinical method) or Nugent's score (a laboratory method with higher reproducibility). This study was undertaken to compare the diagnostic ability of the Amsel criteria with that of Nugent's score among patients presenting with abnormal vaginal discharge. Methodology: The study was conducted at the Medical College in Kolkata, India to determine the prevalence of patients with bacterial vaginosis and their demographic profile. Subjects attending the outpatient department presenting with abnormal vaginal discharge were evaluated for the presence of bacterial vaginosis by Amsel criteria and Nugent's score. Results: Prevalence of bacterial vaginosis was 24% by Nugent's score. In comparison, Amsel criteria had sensitivity of 66.67%, specificity of 94.74%, positive predictive value of 80% and negative predictive value of 90%. There was no perfect inter-rater agreement between the Amsel criteria and Nugent's score (Kappa = 0.58). Presence of clue cells correlated best with a positive diagnosis by Nugent's score while the amine test (whiff test) had the lowest correlation. Conclusion: Although the Amsel criteria method is a convenient and inexpensive means of diagnosing bacterial vaginosis, it is not always reliable.  Alternative reliable and inexpensive diagnostic methods that unify clinical and microbiological parameters, thus increasing sensitivity while retaining specificity, are needed.

The saturation magnetization (M S ), antiferromagnetic transition point (T N ), and the off-center displacements of Bi and Fe ions have been measured as a function of particle size in nanoscale BiFeO 3 . T N decreases down to $550 K for particles of size $5 nm from $653 K in bulk, while M S rises by more than an order of magnitude. Analysis of crystallographic structure from Rietveld refinement of x-ray diffraction patterns shows significant rise in off-center displacements of Bi (d Bi ) and Fe (d Fe ) ions within a unit cell with the decrease in particle size. The net unit-cell polarization P S too, is found to be larger in nanoscale regime.

From the measurement of dielectric, ferroelectric, and magnetic properties we observe simultaneous ferroelectric and magnetic transitions around ∼600 K in orthorhombic LuFeO 3 . We also observe suppression of the remanent polarization by ∼95% under a magnetic field of ∼15 kOe at room temperature. The extent of suppression of the polarization under magnetic field increases monotonically with the field. These results show that even the orthorhombic LuFeO 3 is a room temperature multiferroic of type-II variety exhibiting quite a strong coupling between magnetization and polarization.PACS numbers: 75.80.+q, 75.75.+a, 77.80.-e The magnetoelectric multiferroics with strong crosscoupling between ferroelectric and magnetic order parameters have attracted a lot of attention during the last one decade because of their potential in radically enhancing the functionalities of the spintronics-based devices for many, including bio-medical, applications. 1 A room temperature multiferroic, for obvious reasons, is always the most sought-after compound. Apart from BiFeO 3 , other systems such as CuO3] have also been identified as potential high temperature multiferroic compounds. In recent time, hexagonal LuFeO 3 is found to exhibit multiferroicity at room temperature. 4 Coexistence of ferrimagnetic and ferroelectric orders was reported in orthorhombic LuFe 1−x Mn x O 3 as well. 5 However, in none of these recent work direct measurement of the multiferroic coupling has been attempted. In this Letter, we show that even the pure orthorhombic-LuFeO 3 , in bulk form, exhibits large magnetoelectric multiferroic coupling at room temperature. The remanent polarization (P r ) is suppressed by ∼95% under a magnetic field of ∼15 kOe. The extent of suppression of P r increases monotonically with the increase in magnetic field. The ferroelectric and magnetic transitions are simultaneous around ∼600 K indicating magnetic structure driven ferroelectricity. This observation signfies that the orthorhombic LuFeO 3 is a multiferroic of type-II variety.The structurally nonpolar orthoferrites such as SmFeO 3 , YFeO 3 , LuFeO 3 etc. exhibit small yet finite ferroelectric polarization because of noncollinear spin structure with canted antiferromagnetic order. [6][7][8] This magnetic order induces a spin current 9 via spinorbit-coupling driven antisymmetric exchange interaction along the Fe 3+ -O 2− -Fe 3+ pathway. The spin current ( j s ) in such a noncollinear magnetic structure breaks the a) Electronic mail: dipten@cgcri.res.in centrosymmetry of the electronic charge density distribution and yields a finite polarization ( P ∝ j s ). 9,10 These compounds, where magnetism drives ferroelectricity, belong to the type-II category of the multiferroics. Interestingly, unlike the well-known perovskite manganites such as TbMnO 3 or DyMnO 3 , the rare-earth orthoferrites exhibit the ferroic transitions at well above the room temperature. In fact, for many of these orthoferrites, the magnetic and ferroelectric transition points (T N and T C , respectively) ar...