Superparamagnetic iron

Keywords magnetic resonance, oxide glasses, iron, superparamagnetism,... 

The crystal stmcture of the intermediate is not well understood. The final iron phase is termed superparamagnetic because the particle size is too small to support ferromagnetic domains. At low rates, the discharge occurs in two steps separated by a small voltage difference. At high rates, however, the two steps become one, indicating that the first step is rate limiting, ie, the second step (eq. 34) occurs immediately after formation of the intermediate (eq. 33). 

Figure 6.13 shows the Mossbauer spectra of ferritin [51], which is an iron-storage protein consisting of an iron-rich core with a diameter around 8 nm with a structure similar to that of ferrihydrite and which is surrounded by a shell of organic material. At 4.2 K essentially all particles contribute to a magnetically split component, but at higher temperatures the spectra show the typical superposition of a doublet and a sextet with a temperature dependent area ratio. At 70 K the sextet has disappeared since all particles have fast superparamagnetic relaxation at this temperature. 

Muller, K., Skepper, J.N., Posfai, M., Trivedi, R., Howarth, S., Corot, C., Lancelot, E., Thompson, P.W., Brown, A.P., and Gillard, J.H. (2007) Effect of ultrasmall superparamagnetic iron oxide nanoparticles (Ferumoxtran-10) on human monocyte-macrophages invitro. Biomaterials, 28 (9), 1629-1642. 

FIGURE 11.9 An extremely broad EPR signal form the superparamagnetic core in ferritin. The spectrum is from Pyrococcus furiosus ferritin. The sharp signal at g = 4.3 (circa 1570 gauss) is from a trace of contaminating dirty iron. ... 

The chemical composition of particles can be just as varied as their shape. Commercial particles can consist of polymers or copolymers, inorganic constructs, metals and semiconductors, superparamagnetic composites, biodegradable constructs, and synthetic dendrimers and dendrons. Often, both the composition of a particle and its shape govern its suitability for a particular purpose. For instance, composite particles containing superparamagnetic iron oxide typically are used for small-scale affinity separations, especially for cell separations followed by flow cytometry analysis or fluorescence-activated cell sorting (FACS). Core-shell semiconductor particles, by... 

Figure 5.12 In situ Mossbauer spectra of a reduced Felr/Si02 catalyst at a reaction temperature of 525 K and during CO hydrogenation when the catalyst is in its steady state (methanol-producing state). The bottom spectrum represents the difference between the two upper spectra it is characteristic of an iron carbide in superparamagnetic state (courtesy of Hyung Woo, adapted from [8]).

Figure 1. MSC accumulate within the scar area. MSC fed with superparamagnetic iron oxide nanoparticles and injected into the border zone of infarcted myocardinm migrate into the infracted area.

Ittrich, H., Lange, C., Dahnke, H., Zander, A.R., Adam, G. and Nolte-Ernsting, C. (2005) Labeling of mesenchymal stem cells with different superparamagnetic particles of iron oxide and detectability with MRI at 3T. Rofo 177, 1151-63. 

Different Mossbauer and magnetometric studies have shown the superparamagnetism of ferritin iron cores. This property is also typical of ferro-... 

Because the appearance of the superparamagnetic effect depends on the particle size and on the anisotropy constant, it is often displayed at room temperature by iron oxides <10 nm in size, for example, soil iron oxides. Superparamagnetic relaxation may be counteracted by lowering the temperature and thereby increasing x. Superparamagnetic particles will usually be ordered below a blocking temperature,Tb, which is ... 

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