Superparamagnetic particles

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. 

The magnetic susceptibility relaxation is usually more important for than for Ti. In fact, this mechanism is often dominant in determining the proton linewidth in paramagnetic proteins at high magnetic fields (3). Gillis and co-workers have recently developed a theory for the related case of proton linewidth in colloidal solutions of so-called superparamagnetic particles (54,55). 

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 ... 

The applications of EPR to determine the particle size of the Fe2C>3 clusters distributed in MFI frameworks was illustrated by Ferretti et a/.145-146 By plotting the peak-to-peak line width of the Fe3+ signal as a function of 1/T, the authors explain how an estimate of the dimension of the superparamagnetic particles can be found in this case 30 nm. While only particles with dimensions greater than 10 nm can be analysed by this approach, this work demonstrates the diversity of information that can be extracted from the simple X-band powder spectrum of Fe3+. 

Kantor, A. B., Gibbons, I., Miltenyi, S., and Schmitz, J. (1998) Magnetic cell sorting with colloidal superparamagnetic particles, in Cell Separation Methods and Applications (Recktenwald, D., and Radbruch, A., eds.), Marcel Dekker, Inc., New York, pp. 153. 

III. Low-Frequency Nonlinear Susceptibilities of Superparamagnetic Particles in Solid Matrices A. Linear and Cubic Dynamic Susceptibilities Numerical Solutions... 

III. LOW-FREQUENCY NONLINEAR SUSCEPTIBILITIES OF SUPERPARAMAGNETIC PARTICLES IN SOLID MATRICES... 

The idea of the magnetic stochastic resonance has emerged in a natural way first as a theoretical issue [25-27] and shortly afterward was supported by some experimental evidence [28,31]. A consistent theoretical treatment of magnetic SR in a superparamagnetic particle in the framework of the linear response theory was developed in Refs. 29 and 30. 

Resonance-like suppression of the higher harmonics in the response spectrum of a superparamagnetic particle is investigated. Using a nonperturbative approach, we analyze the steady processes that take place under arbitrary values of the DC (bias) and AC (excitation) strengths. The results show that the suppression effect is equally achieved on varying either noise (temperature) or force (external field intensity) or by a combination of both. In the fundamental aspect, we surmise... 

Figure 4.31. Schematic representation of a superparamagnetic particle in the egg model.

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