Giant and time-dependent magnetocaloric effect in high-spin molecular magnets

We have measured and calculated the magnetocaloric effect in macroscopic samples of oriented high-spin molecular clusters like Mn-12 and Fe-8 as a function of the temperature and both the intensity and the sweeping rate of the applied magnetic field. We have observed a high magnetic entropy variation around the blocking temperature of the magnetic moment of molecules and calculated the shift of the entropy variation and cooling temperature, with the sweeping rate of the magnetic field. (C) 2000 American Institute of Physics. [S0003-6951(00)02746-7].