Magnetic properties of Co-doped Eu8Ga16Ge30 type-I clathrate

Abstract

Type-I Eu8Ga16Ge30 clathrate is a stable functional material with special magnetocaloric properties, mainly derived from the 4f magnetism of Eu ions. However, the influence of cage atoms, especially 3d magnetic atoms, on the magnetic properties of Eu8Ga16Ge30 is still lackof study. Co-doped Eu8Ga15Co1Ge30 was synthesized creatively by using arc method. It's magnetic properties have been investigated and compared with that of Co-free Eu8Ga16Ge30. Because Co ion has magnetic moment, its joining will introduce a new 3d-4f interaction into the lattice. This study can enrich the understanding of RKKY interaction between Eu ions with larger distances. The substitution of Co for Ga atoms on the cage frame results in the decrease of the ferromagnetic ordering temperature (TC) from 34.7 to 31.1 K. By fitting the M−H curves using Brillouin function, the exchange parameter λ was obtained. The decrease of λ from 0.25 to 0.21 T·emu−1·g due to the Co doping is thought to be the inherentreason of the TC decrease. For a magnetic field change from 0 to 3 T, the maximum magnetic entropy change -ΔSMmax around TC for Eu8Ga15Co1Ge30 is 5.92 J/kg·K, which is a little smaller than the value 6.0 J/kg·K of Eu8Ga16Ge30. This could be attributed to the decrease of the saturation magnetic moment. The critical exponents β, γ and δ around TC, the -ΔSM(H) behaviors below, at and above TC are analyzed and discussed.