  Thermomechanical cycles with a ferroelectric working substance convert heat
to electrical energy. As shown here, magnetoelectrically coupled
ferroelectric/ferromangtic composites (also called multiferroics) add new
functionalities and allow for an efficient thermal energy harvesting at room
temperature by exploiting the pyroelectric effect. By virtue of the
magnetoelectric coupling, external electric and magnetic fields can steer the
operation of these heat engines. Our theoretical predictions are based on a
combination of Landau-Khalatnikov-Tani approach (with a
Ginzburg-Landau-Devonshire potential) to simulate the ferroelectric dynamics
coupled to the magnetic dynamics. The latter is treated via the
electric-polarization-dependent Landau-Lifshitz-Gilbert equation. Performing an
adapted Olsen cycle we show that a multiferroic working substance is
potentially much more superior to sole ferroelectrics, as far as thermal energy
harvesting using pyroelectric effect is concerned. Our proposal holds promise
not only for low-energy consuming devices but also for cooling technology.
