Comparison of substitution of Si for Ge and Ga in Eu8Ga16Ge30: Magnetic measurement and fitting

Abstract

Nominal Eu8Ga12Si4Ge30 and Eu8Ga16Ge26Si4 were synthesized by using ARC + MS method. XRD and EDS analysis confirmed that Si enters the lattice. Substitution of Si for Ga reduces TC from 35 K to 20 K. But the substitution of Si for Ge only has little effect on TC. It is about 30 K for Eu8Ga16Ge26Si4. The decrease of TC is beneficial to the increase of magnetic entropy change. So the maximum value of magnetic entropy change −ΔSMmax around TC under magnetic field change ΔH=3T increases to 7.6 and 6.1 J/kg﹒K for Eu8Ga12Si4Ge30 and Eu8Ga16Ge26Si4, respectively. They are both larger than the 6.0 J/kg﹒K of Eu8Ga16Ge30, especially Eu8Ga12Si4Ge30. So Ga is more important than Ge in terms of the physical properties of Eu8Ga16Ge30. The M − H data were fitted by Brillouin function. A series of parameters such as exchange parameter λ in Hexch = λM，the Lande factor g and total angular momentum quantum number J were obtained. Using these parameters, TC and −ΔSMmax were calculated and compared with the above values.