Origin and tuning of the magnetocaloric effect for the magnetic   refrigerant MnFe(P1-xGex)
  Neutron diffraction and magnetization measurements of the magneto refrigerant Mn1+yFe1-yP1-xGex reveal that the ferromagnetic and paramagnetic phases correspond to two very distinct crystal structures, with the magnetic entropy change as a function of magnetic field or temperature being directly controlled by the phase fraction of this first-order transition. By tuning the physical properties of this system we have achieved a maximum magnetic entropy change exceeding 74 J/Kg K for both increasing and decreasing field, more than twice the value of the previous record. 
Danmin Liu, Ming Yue Jiuxing Zhang, T. M. McQueen, Jeffrey W. Lynn,   Xiaolu Wang, Ying Chen, Jiying Li, R. J. Cava, Xubo Li...