  Hysteresis is more than just an interesting oddity, which occurs in materials
with a first-order transition. It is a real obstacle on the path from existing
lab-scale prototypes of magnetic refrigerators towards commercialization of
this potentially disruptive cooling technology. Indeed, the reversibility of
the magnetocaloric effect, being essential for magnetic heat pumps, strongly
depends on the width of the thermal hysteresis and therefore it is necessary to
understand the mechanisms causing hysteresis and to find solutions how to
minimize losses associated with thermal hysteresis in order to maximize the
efficiency of magnetic cooling devices. In this work, we discuss fundamental
aspects, which can contribute to thermal hysteresis and we are developing
strategies for at least partially overcoming the hysteresis problem in some
selected classes of magnetocaloric materials with large application potential.
Doing so, we refer to the most relevant classes of magnetic refrigerants
La-Fe-Si-, Heusler- and Fe2P-type compounds.
