The exchange coupling as being responsible for ferromagnetism is not the mutual magnetic interaction between two elementary magnetic dipoles. To show this, calculate (a) the magnitude of the magnetic field a distance of 9.7 nm away, along a dipole axis, from an atom with magnetic dipole moment 2.0 × 10-23 J/T, and (b) the minimum energy required to turn a second identical dipole end for end in this field.
The exchange coupling as being responsible for ferromagnetism is not the mutual magnetic interaction between two...