Tuning RScT (R = rare-earth and T = transition metal) materials to the edge of stability*

We report here the interplay between the crystal structure and magnetism in the series of RTX materials (R = rare-earth, T = transition metal and X = p-block element). We demonstrate that the CeScSi-type adopted by GdScGe and CeFeSi-type by GdScSb coexist over a limited range of compositions. Sb for Ge substitutions in GdScGe result in an anisotropic expansion of the unit cell of the parent that is most pronounced along the c-axis. Such expansion acts as the driving force for the instability of the double layer CeScSi-type structure of GdScGe. Extensive, yet limited Sb substitutions lead to a strong reduction of the Curie temperature, but without affecting the saturation magnetization. At x_Sb = 0.7, the appearance of an antiferromagnetic (AFM) phase coincides with the CeFeSi-type . The electronic structure calculations for x_Sb = 0.75 indicate that the key factor in the conversion of the ferromagnetic CeScSi-type to the antiferromagnetic CeFeSi-type structure is the disappearance of the induced magnetic moment on Sc.