Comparison of the Mn and Ni doped Eu8Ga16Ge30 type-I clathrates

The Mn and Ni-doped type-I clathrates with nominal compositions of Eu8Ga15M1Ge30 (M = Mn, Ni) were prepared by the ARC technique. The incorporation of 3d metals into the cage frame leads to the decrease in lattice parameters. The compounds undergo a paramagnetic to ferromagnetic transition at 32.3 K for Eu8Ga15M1Ge30 and 32.5 K for Eu8Ga15M1Ge30, which are both about 2.5 K lower than that of the Mn/Ni-free Eu8Ga15M1Ge30 . These transitions were identified to be second-order through the slope of the Arrott plot curves according to the Banerjee's criteria. In addition, the improvement of magnetic entropy change is observed due to doping. The maximum value of the magnetic entropy change -Delta S-M(max) of Eu8Ga15M1Ge30 is 6.64 J/kg K around T-c for a field change of 3T. This magnetic entropy change is 14.5% higher than that of Mn/Ni-free Eu8Ga15M1Ge30 . Mn-doping can result in a higher magnetic entropy change than Ni-doping. The -Delta S-M(max) of Eu8Ga15M1Ge30, is only 6.13 J/kg K around T-c for a field change of 3 T, in spite of the similar T-c as Eu8Ga15M1Ge30. The estimated saturation magnetic moments per Eu2+ ion are 6.79 and 6.47 mu(B) for Eu8Ga15M1Ge30Eu 8 Ga 15 Mn , and Eu8Ga15M1Ge30, respectively. The lager saturation magnetic moment is the major reason for the higher -Delta S-M(max) value of Eu8Ga15M1Ge30.