Das Lorentzfeld und die Dipolkopplung

The field at the center of a Lorentz-sphere due to all dipoles within this sphere has been calculated, assuming inhomogeneous orientations of the dipoles in the sphere, as one must expect in real crystals. This field has very often been neglected. The calculation shows the existence of a coupling field which stiffens the dipole directions against localized torques due to “distortion fields”. In the case of ferromagnetism, one can calculate the coupling field of an expanded Lorentz volume. This is analogous to the quantummechanical exchange field, which is due to the excess exchange energy. In many cases the above dipole coupling field is more important than the wellknown exchange field because the “dipole coupling constants” exceed the exchange constant by orders of magnitude.