The Magnetocaloric Effect in Gd-Doped Eu6.5Gd1.5Ga16Ge30 Type-I Clathrate

In this paper, magnetic Gd atom is firstly introduced into the type-I clathrate Eu8Ga16Ge30. A sample with nominal composition Eu6.5Gd1.5Ga16Ge30 was synthesized by combining arc melting (ARC) and melt spinning (MS) techniques. The lattice parameter decreases due to the smaller ionic radius of Gd3+ than that of Eu2+. The sample experiences a paramagnetic to ferromagnetic magnetic transition at about 31.5 K. It is about 3 K lower than that of Eu8Ga16Ge30. Under the applied magnetic field of 3 T, the maximum magnetic entropy change -Delta S-M(max) around T-C is 4.8 J/kg.K. This value is much lower than that of the undoped Eu8Ga16Ge30 (6.0 J/kg.K). The reduction of saturation magnetization is mainly responsible for the reduction of magnetic entropy change. The large critical exponent beta confirms the inevitability of the decrease of magnetic entropy change. On the other hand, Gd-doping strengthens the small second magnetic transition at low temperature. Coexistence of two magnetic transitions widens the -Delta S-M(T) curves and results in large values of refrigerant capacity (RC) and relative cooling power (RCP).

Automated summary

This paper introduces magnetic Gd atom into type-I clathrate Eu8Ga16Ge30 for the first time, and finds that Gd doping not only reduces the magnetic entropy change of the sample, but also strengthens the second magnetic transition at low temperature, resulting in larger refrigerant capacity and relative cooling power.