Magnetocaloric and structural properties of SmMn2Ge2

We have performed detailed magnetization, specific heat and powder X-ray diffraction measurements under magnetic fields, for obtaining information on the magnetic and the structural properties of re-entrant ferromagnet SmMn2Ge2 with the ThCr2Si2-type tetragonal structure. The lattice parameter a decreases by about 0.1%, while the parameter c increases slightly by about 0.02% in the antiferromagnetic (AFM) state, compared with the ferromagnetic (FM) and re-entrant ferromagnetic (RFM) states. In the AFM state, the structural distortion recovers by applying a magnetic field, accompanied with the metamagnetic transition from the AFM to the forced FM states. The results of a magnetocaloric effect indicate that the magnetic entropy change at these phase transitions is mainly due to the change of the Sm magnetic state.