On the conventional and rotating magnetocaloric effects in multiferroic   TbMn2O5 single crystals
  Solid state-refrigerants have generated worldwide interest owing to their growing potential for use in efficient and green cooling devices. Caloric effects could be obtained by manipulating their degrees of freedom such as magnetization, electric polarization and volume using a variable external field. In conventional magnetocaloric refrigeration systems, the magnetocaloric effect is exploited by moving the active material in and out of the magnetic field source. Here we demonstrate that a giant and reversible magnetocaloric effect can be generated simply by rotating the multiferroic TbMn2O5 single crystal around its b axis in a relatively low constant magnetic field applied in the ac plane. For a magnetic field applied along the easy axis a, we report an entropy change of 12.25 J/kg K at about 10 K in a field change of 5 T which is 100 times larger than that found when the field is applied along the hard axis c. When the TbMn2O5 is rotated with the field remaining in the ac plane, the associated adiabatic temperature change reaches minimum values of 8 K and 14 K under 2 T and 5 T, respectively. This giant rotating magnetocaloric effect in TbMn2O5 is caused by the colossal anisotropy of the entropy change, the enhancement of the magnetization under relatively moderate magnetic fields and the lower magnitude of specific heat. On the other hand, the application of the coherent rotational model demonstrates that the rotating magnetocaloric effect exhibited by TbMn2O5 does not originate directly from the magneto-crystalline anisotropy. Our results should inspire and open new ways toward the implementation of compact, efficient and embedded magnetocaloric devices for low temperature and space application. Its potential operating temperature range of 2 to 30 K makes it a great candidate for the liquefaction of hydrogen. 
M. Balli, S. Jandl, P. Fournier, D. Z. Dimitrov
cond-mat.mtrl-sci