The _analog_[14] of ferroelectricity is ferromagnetism. A converter
employing similar principles to those in ferroelectricity can be made
using an electrical _inductance_ with a ferromagnetic core. When the
temperature of the ferromagnetic material is raised above its Curie
point, its magnetic _permeability_ drops quickly, causing the magnetic
field to collapse partially. Energy may be delivered to an external load
during this change. Instead of energy being stored in an electrostatic
field, it is stored in a magnetic field.
Ferroelectric and thermomagnetic conversion both represent a class of
energy transformations which involve internal molecular or crystalline
rearrangements of solids. There is no change of phase as in a steam
engine, but the energy changes are there nevertheless. In thermodynamics
such internal geometrical changes are called _second-order_ transitions,
as opposed to the _first-order_ transitions observed with heat engines
using two-phase working fluids like water/steam.