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A b s t r a c t -A theory is set up to calculate anisotropy fields in assemblies of fine magnetic particles from remanence curves. The formallsm takes i n t o a c c o u n t t h e e f f e c t s of thermal fluctuations. With the help o f this approach a n i s o t r o p y f i e l d s o f m i c r o c r y s t a l l i n e a n d nanocrystalline bariumhexaferrite particles are determined.

Using a kinetic equation method the growth rate of steps in dependence on the Jackson-Temkin factor, the deviation from equilibrium and the step orientation is determined. Diffusion processes within the step structure are included. The results obtained are compared with those of Monte-Carlo simulations. The method is generalized to non-Kossel crystal structures and applied to the growth rate anisotropy of steps on garnet (110)-surfaces. Unter Verwendung einer Methode der kinetischen Gleichungen wird die Wachstumsrate von Stufen in Abhingigkeit vom Jackson-Temkin-Faktor, der Oberschreitung und der Orientierung der Stufen bestimmt. Diffusionsprozesse innerhalb der Stufenstruktur sind eingeschlossen. Die erhaltenen Resultate werden mit jenen der Monte-Carlo-Simulation verglichen. Die Methode wird auf Nicht-Kossel-Kristalle verallgemeinert und auf die Anisotropie der Wachstumsrate von Stufen auf (110)-Granatfliichen angewendet.

Abstract-C o -T i -S n -Ge s u b s t i t u t e dM-ty pe bariumhexaferrite powders with mean grain sizes between about 10 nm and about 1 Fm and a narrow size distribution were prepared reproducibly by means of a modified glass crystallization method.At annealing temperatures between 560 and 580 *C of the amorphous flakes nanocrystalline particles grow. They behave superparamagnetically at room temperature and change into stable magnetic single domains at lower temperatures. The magnetic volume of the powders is considerably less than the geometric one. However, the effective anisotropy fields are larger by a factor of two to three.

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