Magnetic Properties of Eu8GaxGe46−x (Nominal x = 16, 14, and 12) Type-I Clathrates

Abstract

Melt-spinning technique can widen the range of Ga content in Eu8GaxGe46−x type-I clathrate. In this paper, it was used to obtain Eu8GaxGe46−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 TC is observed. It is 34.7 K, 27.0 K, and 20.0 K for Eu8GaxGe46−x with nominal x =16, 14, and 12, respectively. However, the saturation magnetic moment μsat and effective magnetic moment μeff are not greatly affected by the change of Ga content. The decrease of TC is mainly attributed to the decrease of molecular field coefficient λ, which can be calculated by fitting the relation curve between exchange mean field Hexch 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 TC is beneficial to the increase of magnetic entropy change, the maximum value of magnetic entropy change ( $$ - \Delta S_{{_{\text{M}} }}^{ \text{max} } $$ ) around TC when $$ \Delta H $$ = 3 T increases from 6.0 to 7.0 J/(kg K) as x decreases from 16 to 12.