Magnetic Properties of Eu₈Ga_xGe_46−x (Nominal x = 16, 14, and 12) Type-I Clathrates

Melt-spinning technique can widen the range of Ga content in Eu₈Ga_xGe_46−x type-I clathrate. In this paper, it was used to obtain Eu₈Ga_xGe_46−x with nominal 16 ≥ x ≥ 10. Three samples with nominal x = 16, 14, and 12 are discussed in detail. Their actual Ga contents detected by EDS are 14.3, 13.4, and 11.5, which is a relatively wide range that has not been reported before. The decrease of Ga content results in the decrease of lattice parameter a. Moreover, a huge decline of the ferromagnetic transition temperature T_C is observed. It is 34.7 K, 27.0 K, and 20.0 K for Eu₈Ga_xGe_46−x with nominal x =16, 14, and 12, respectively. However, the saturation magnetic moment μ_sat and effective magnetic moment μ_eff are not greatly affected by the change of Ga content. The decrease of T_C is mainly attributed to the decrease of molecular field coefficient λ, which can be calculated by fitting the relation curve between exchange mean field H_exch and magnetization M. The fitted λ values are 0.25, 0.18, and 0.16 for samples with nominal x = 16, 14, and 12. Because the decrease of T_C is beneficial to the increase of magnetic entropy change, the maximum value of magnetic entropy change (\( - \Delta S_{{_{\text{M}} }}^{ \text{max} } \)) around T_C when \( \Delta H \) = 3 T increases from 6.0 to 7.0 J/(kg K) as x decreases from 16 to 12.