The Field-Temperature Phase Diagram of the Heavy Fermion Compound Ce$_2$Ge$_2$Mg

The heavy fermion metal Ce$_2$Ge$_2$Mg has a layered structure with the Ce nearest neighbor pairs arranged orthogonally to one another in the tetragonal $a$-$b$ plane, a structure topologically equivalent to the Shastry-Sutherland lattice (SSL). This material is thought to be more two dimensional than other $R_2T_2X$ SSL compounds such as Yb$_2$Pt$_2$Pb, due to the relatively long distance along the $c$-axis between Ce atoms in adjacent SSL planes. The magnetic phase diagram of Ce$_2$Ge$_2$Mg has been determined for magnetic fields in the SSL plane and along the $c$-axis, for temperatures from the antiferromagnetic transition at $T = 9.4$ K in zero applied field down to $T = 1.8$ K and fields as high as 14 T using magnetization, resistance, and heat capacity. Our measurements show a complex phase diagram with field suppressing the antiferromagnetic transition and the emergence of several ordered phases. These phases are possible evidence for singlet-to-triplet excitations in the Ce dimers. \\ This project was supported by NSF-DMR-1310008