4. Thermomagnetic effects

4.1 Fundamental principles

The entropy of a magnetic solid is the sum of two contributions:

• a magnetic contribution due to directional disorder of magnetic moments ;

• the contribution of thermal vibrations of the crystal lattice (phonons), explained simply as lattice contribution in the following, found in all solids.

By applying a magnetic induction B at constant temperature, we reduce the magnetic entropy S _M in the same way as the entropy of a gas is reduced by isothermal compression.

In algebraic value, we have :