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An analytic expression is given for the magnetometric demagnetizing factors of the general rectangular prism, with special emphasis on the particular case of a square cross section. It is argued that this demagnetizing factor should be used in numerical computations that assume such prisms, when comparing the results with the theoretical study of ellipsoids.

Magnetostatic resonance modes are usually calculated by assuming that the exchange energy is negligible compared to the magnetostatic energy. It is shown that in the other extreme, when the magnetostatic energy is small compared to the exchange energy, the resonance modes are a quadratic function of the reciprocal size.

The nucleation field is calculated for a small ferromagnetic prolate spheroid as a function of its size, its elongation, and the angle between the applied field and the spheroid axis. If there is no other switching mode except for magnetization curling and coherent rotation, these results probably represent the coercivity. The calculation is rigorous only for an isotropic particle, but a first order approximation is also given for a uniaxial or cubic anisotropy whose easy axis is parallel to the long axis of the spheroid.

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