Magnetic ordering in GdAuAl4Ge2 and TbAuAl4Ge2: Layered compounds with triangular lanthanide nets

We report the synthesis and magnetic properties of GdAuAl4Ge2 and TbAuAl4Ge2, where temperature and magnetic field dependent magnetization, heat capacity, and electrical resistivity measurements reveal that both compounds exhibit several magnetically ordered states at low temperatures, with evidence for magnetic fluctuations extending into the paramagnetic temperature region. For magnetic fields applied in the ab-plane there is particularly rich behavior, with several ordered state regions that are separated by metamagnetic phase transitions. Despite Gd being an isotropic S-state ion and Tb having an anisotropic J-state, there are similarities in the phase diagrams for the two compounds, suggesting that factors such as the symmetry of the crystalline lattice, which features well separated triangular planes of lanthanide ions, or the Ruderman–Kittel–Kasuya–Yosida interaction control the magnetism. We also point out similarities to other centrosymmetric compounds that host skyrmion lattices such as Gd2PdSi3, and propose that the LnAuAl4Ge2 family of compounds are of interest as reservoirs for complex magnetism and electronic behaviors.