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A method for the analysis of temperature and field dependent magnetization data near the Curie temperature T C is devised, which allows the reliable determination of critical

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Silver nanoparticles (AgNPs) were synthesized by chemical reduction of Ag + ions (from silver nitrate AgNO 3 ), using aqueous or ethanolic Aloe vera extracts as reducing, stabilizing, and size control agent. The nanoparticles' sizes were between 2 and 7 nm for ethanolic extract and between 3 and 14 nm for aqueous extract, as measured by High-Resolution Transmission Electron Microscope (HRTEM). The antibacterial activity against a mesophilic microorganism, Kocuria varians, a Gram-positive coccus, was measured by counting bacterial colonies in agar plate for both extracts. We found that 4% effective concentration is the lowest concentration that completely inhibited visible growth. Mercury removal was investigated by Atomic Absorption Spectroscopy (AAS) measurements, where it was shown that it is not necessary to use high concentrations of nanoparticles for effective removal of mercury inasmuch as with a 20% V/V concentration of both extracts; the Hg(II) removal percentage was above 95%. These results show that the mercury remaining unremoved from the different essays is below the level allowed by World Health Organization (WHO) and the Environmental Protection Agency (EPA).

We report on the magnetic and superconducting properties of La 0.7 Ca 0.3 MnO 3 /YBa 2 Cu 3 O 7 ͑LCMO/ YBCO͒ superlattices. For a constant LCMO layer thickness of 6 unit cells ͑u.c.͒, resistance and susceptibility measurements show superconductivity for YBCO layer thickness in excess of 4 unit cells. The critical temperature increases with YBCO thickness, and a T c of 58 K is found for a YBCO thickness of 10 unit cells. Magnetization measurements show a ferromagnetic transition at 100 K in a (LCMO 6 u.c. /YBCO 5 u.c. ͒ 15 bilayer superlattice, and a depressed value of the saturation magnetization of 20 emu cm Ϫ3. These results are discussed in terms of interface disorder ͑analyzed by x-ray diffraction and transmission electron microscopy͒ and of the possible interaction between magnetism and superconductivity.

Superlattices of antiferromagnetic (AF) La1∕3Ca2∕3MnO3 and ferromagnetic (F) La2∕3Ca1∕3MnO3 were grown using sputtering technique. The AF layer thickness ranged between 3.9nm⩽tAF⩽15.6nm while the F layer thickness was kept constant (7.8 nm). Hysteresis measurements after field cooling, show an exchange bias up to a temperature of ∼100K. Surprisingly, the saturation magnetization increases with antiferromagnetic layer thickness and can exceed the expected bulk value for the La2∕3Ca1∕3MnO3 composition, whereas the interface coupling energy between the AF and F layers derived from the exchange bias is constant. This suggests that magnetization depth profile extends beyond the chemical doping interface.

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We have measured structural, magnetic and, magneto transport properties of heterostructures consisting of La1–xCaxMnO3 ferromagnetic (FM) layers (x = 0.33) and antiferromagnetic (AF) layers (x = 0.67). FM/AF superlattices were grown by a high‐pressure sputtering technique on (001) oriented SrTiO3 substrates. We have systematically varied the thickness of the ferromagnetic layers, while maintaining the thickness of the antiferromagnetic layers fixed. The total superlattice thickness was held approximately constant. The XRD analysis confirmed the existence of the superlattice structure by the multiple satellite peaks around the 00l manganite Bragg reflections. We have done field cooling (FC) and zero field cooling (ZFC) magnetization, and magneto resistance measurements at temperatures between 10 K and 280 K. The existence of an exchange bias effect at temperatures below the Neel temperature of the AF layer was revealed by magnetization loops after field cooling. The exchange bias field magnitude Hex exhibited exponential temperature dependence below the blocking temperature, as well as an inverse proportionality with the ferromagnetic layer thickness. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)