Micromagnetic and morphological characterization of heteropolymer human ferritin cores.

The physical properties of iron-reconstituted and genetically engineered human heteropolymer ferritins were investigated. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron energy-loss spectroscopy (EELS), and Fe Mössbauer spectroscopy were employed to ascertain (1) the microstructural, electronic, and micromagnetic properties of the nanosized iron cores, and (2) the effect of the H and L ferritin subunit ratios on these properties. Mössbauer spectroscopic signatures indicate that all iron within the core is in the high spin ferric state.

Size- and composition-dependent radio frequency magnetic permeability of iron oxide nanocrystals.

We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals.

A comparative Mössbauer study of the mineral cores of human H-chain ferritin employing dioxygen and hydrogen peroxide as iron oxidants.

Ferritins are ubiquitous iron storage and detoxification proteins distributed throughout the plant and animal kingdoms. Mammalian ferritins oxidize and accumulate iron as a ferrihydrite mineral within a shell-like protein cavity. Iron deposition utilizes both O(2) and H(2)O(2) as oxidants for Fe(2+) where oxidation can occur either at protein ferroxidase centers or directly on the surface of the growing mineral core.

Size-dependent magnetic properties of single-crystalline multiferroic BiFeO3 nanoparticles.

As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period length of approximately 62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.