Uniform magnetization, ferrofluids

In a typical ferrofluid the particles will have median radii 2-10 nm so that thermal energy overcomes magnetostatic interaction between the particles and prevents aggregation. The single domain particles are considered to be in a state of uniform magnetization with magnetic moment... 

A method for the production of stable iron colloids in solution has been developed." Sonication of Fe(CO)5 in the presence of a polyvinylpyrrolidone (PVP) stabilizer yielded an iron colloid with a particle size ranging from 3 to 8nm, while sonication in oleic acid yielded colloids with a uniform size of 8nm. Heating of the resulting colloids yielded bcc-Fe. The colloids were superparamagnetic, with a saturation magnetization of 101 emug , compared to a saturation magnetization of 123 emu g for a typical iron-based ferrofluid. 

Abstract. The appearance of labyrinthine patterns in ferrofluids is studied theoretically. An approximate theory based upon the use of a uniform demagnetization field predicts a first-order transition with hysteresis. A more accurate approach indicates that these predictions are caused by the uniform approximation. Even the existence of a minimum field strength required to induce the labyrinthine pattern cannot be confirmed by the more accurate calculations. The infiuence of the uniform approximation upon the calculated results is explained by a study of the evolution of the magnetic energy as a function of the pattern size. 

Recently, we have developed several schemes to improve the accuracy of the magnetic energy term [14,15]. The main difference between these methods and the uniform approach is the calculation of the demagnetization field in the whole volume occupied by the ferrofluid. The only approximation is the... 

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