Demagnetizing fields in magnetic measurements. I. Thin discs

The long-range nature of magnetic dipole interactions leads to a shape dependence of all magnetic properties. In homogeneous ellipsoids, this dependence can be characterized in terms of a simple demagnetizing factor, which depends only on the shape of the body. In all other situations the demagnetizing fields depend on position within the body, and in most cases, also on the magnetic properties of the material. We present calculations on various thin disc-shaped samples, for four different model equations of state, from which demagnetizing corrections in a wide variety of situations can be estimated. The results show that the corrections are generally field and temperature dependent, in contrast to the usual approximation of a constant effective demagnetizing factor. These effects can be quite significant in the analysis of high-resolution magnetic measurements, especially near phase transitions.