Search

A correction to the article "Co-existence of ferrimagnetism and spin-glass state in the spinel Co2SnO4" that was published in the 2013 issue is presented.

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO2 and Al2O3, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co0, CoO, Co3O4, Co2+) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO2 catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al2O3 catalysts. Conversely the Al2O3 supported catalysts gave much higher selectivity towards olefins than Co/SiO2. These results yield the correlation that the presence of Co3O4 yield higher methane selectivity whereas the presence of Co2+ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream. [ABSTRACT FROM AUTHOR]

Synthesis and magnetic properties of nanocrystals (size ≃22 nm) of cubic spinel MgMnO3 with the defect structure [Mg2+][Mg1/32+Mn4/34+□1/3]O4 are reported. Analysis of the magnetization M versus T (2–370 K) and M versus H (up to 65 kOe) data shows a blocking temperature TB≃11 K and an estimated Néel temperature TN∼150 K above which the Weiss temperature θ=-7 K and μ=3.91 μB/Mn4+. For TB

Synthesis and magnetic properties of nanocrystals (size ≃22 nm) of cubic spinel MgMnO3 with the defect structure [Mg2+][Mg1/32+Mn4/34+□1/3]O4 are reported. Analysis of the magnetization M versus T (2–370 K) and M versus H (up to 65 kOe) data shows a blocking temperature TB≃11 K and an estimated Néel temperature TN∼150 K above which the Weiss temperature θ=-7 K and μ=3.91 μB/Mn4+. For TBN, fit of the M versus H data to modified Langevin function yields 35 μB as magnetic moment/particle, resulting from the defect structure. [ABSTRACT FROM AUTHOR]

In this paper, we compare the magnetic relaxation of DNA-coated γFe2 O3 with that of parent 7-nm γFe2 O3 particles by measuring the temperature dependence of AC susceptibilities (χ′ and χ″) at frequency f = 0.1, 1, 10, 100, and 1000 Hz and electron magnetic resonance (EMR) at 9.28 GHz. Changes in the blocking temperature TB (where χ′ peaks) with frequency are analyzed using the relation: TB = Ta + [T0/ln(f0/f)] derived from Vogel-Fulcher relaxation, where Ta(T0) measures the effective energy barrier (interparticle interaction). The fit to the data yields f0 = 1.3 × 1016 Hz, Ta = 2760 K(2960 K), and T0 = 40 K(20 K) for the uncoated (DNA-coated) γFe2 O3. From the relative shift ΔTm of Tm (the temperature where χ″ peaks) with change Δ log f in frequency, the parameterΦ = ΔTm/(TmΔ log f) is determined to be 0.04(0.06) for the uncoated (coated) ΔFe2 O3. These results show only minimal changes in the magnetic dynamics of γFe2 O3 upon DNA coating. [ABSTRACT FROM AUTHOR]

SQUID magnetometry and electron magnetic resonance (EMR) spectroscopy at 9.28 GHz were employed to probe magnetism and surface spin disorder in Fe3 O4 nanoparticles. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed magnetite particles with size ≃8 nm. Magnetization (M) versus temperature studies yielded blocking temperature TB ≃ 170 K in H = 50 Oe. For T > TB, M scales approximately as H/T with μP ≃ 5400 μB as the magnetic moment/particle. At 5 K, the magnitudes of hysteresis loop parameters viz. coercivity Hc ≃ 37 Oe and saturation magnetization M8 = 62 emu/g are considerably smaller than the reported values for larger 150 nm Fe3 O4 particles. In EMR studies, a single symmetric line at g ≃ 2.11 with linewidth ΔH = 850 Oe is observed at 300 K with the g-value and ΔH increasing with decreasing T. These results are interpreted in terms of a disordered surface spin layer of 0.5 nm thickness. [ABSTRACT FROM AUTHOR]

The authors report on carbon-assisted water electrolysis at 300 K which only consumes 9.6 kcal/mol H2O (compared to 56.7 kcal/mol H2O for ordinary electrolysis) using the net reaction C(s)+2H2O(ℓ)→CO2(g)+2H2(g). Carbon-assisted H2 production and its kinetics/energetics are measured at applied potential |E0| between 0.1 and 1.8 V (compared to |E0| >1.25 V required for water electrolysis). Surprisingly, H2 produced per W h is higher at the lower voltages, but longer times are required to produce the same amount of H2 The suggested practical conditions are |E0|≃0.5 V and carbon concentration of 0.08 g/cm3. [ABSTRACT FROM AUTHOR]