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Abstract: We use dynamic susceptometry measurements to extract semiempirical temperature-dependent, 255–400K, magnetic parameters that determine the behavior of single-core nanoparticles useful for SQUID relaxometry in biomedical applications. Volume susceptibility measurements were made in 5K degree steps at nine frequencies in the 0.1–1000Hz range, with a 0.2mT amplitude probe field. The saturation magnetization (M s ) and anisotropy energy density (K) derived from the fitting of theoretical susceptibility to the measurements both increase with decreasing temperature; good agreement between the parameter values derived separately from the real and imaginary components is obtained. Characterization of the Néel relaxation time indicates that the conventional prefactor, 0.1ns, is an upper limit, strongly correlated with the anisotropy energy density. This prefactor decreases substantially for lower temperatures as K increases. We find, using the values of the parameters determined from the real part of the susceptibility measurements at 300K, that SQUID relaxometry measurements of relaxation and excitation curves on the same sample are well described. [ABSTRACT FROM AUTHOR]

The behavior of iron nanoparticles is heavily influenced by their highly reactive surfaces. A better understanding of organic ligand/particle interactions must be achieved in order to synthesize iron nanoparticles with magnetic saturations ( σ sat) equivalent to bulk iron. Even when synthesized using careful, air-free chemistry techniques and ligands more weakly interacting than those often reported in the literature, the magnetic saturation of iron nanoparticles generally only approaches, but not equals, the magnetic saturation of bulk iron. Here, iron nanoparticles are synthesized using Schlenk line chemistry methods and two different weakly interacting ligands: 2,4-pentanedione and hexaethylene glycol monododecylether. These particles have saturation magnetizations slightly lower than bulk iron, which is believed to be caused by interactions between the passivating ligands and the surface of the nanoparticles. Using X-ray absorption fine structure studies, it is shown that oxidized species of iron exist at the nanoparticles' surface and can be attributed to iron/ligand interaction. The percentage of oxidized species scales with the surface to volume ratio of the nanoparticles, and therefore appears limited to the nanoparticle surface. X-ray absorption fine structure analysis also shows that the nanoparticles have an expanded crystalline lattice, which can further impact their magnetic properties. [ABSTRACT FROM AUTHOR]

X‐ray absorption fine structure experiments reveal the interaction between iron nanoparticles synthesized with both 2,4‐pentanedione and hexaethylene glycol monododecylether ligands, and are presented by Todd Monson and co‐workers on page 258. Oxidized species of iron exist at the nanoparticles' surface and can be attributed to iron/ligand interactions. These oxidized species can play a significant role in the nanoparticles' magnetic properties. [ABSTRACT FROM AUTHOR]