Featuring Complex Magnetic Interactions*

Triangular lattices that are occupied by Heisenberg spins provide an environment for magnetic frustration, which often leads to exotic states of matter. By adding interactions that are mediated by conduction electrons (i.e., the RKKY interaction), the breadth of behaviors can be further expanded. In this work, we focus on the synthesis and characterization of a new metallic compound of this sort, Gd₂PdAl₆Ge₄, which was grown as bulk single crystals using molten aluminum-germanium flux. Structural determination was carried out using powder and single-crystal X-ray diffraction, revealing that the compound crystallizes in the R-3m space group with lattice parameters a = 4.1781(6) Å, c = 51.461(13) Å. Temperature-dependent magnetic susceptibility measurements uncover Curie-Weiss behavior followed by antiferromagnetic ordering at T_N1 = 14K and T_N2 = 10K. The ordering temperatures are significantly higher than the fitted Curie-Weiss temperature θ_CW = -0.68K, suggesting that the RKKY mechanism produces competing magnetic exchange interactions. Applied magnetic fields additionally uncover several distinct ordered phases. Further work is still needed to characterize order parameters, but we note that this phase diagram resembles that seen in the triangular net skyrmion lattice compound Gd₂PdSi₃ [1].

1. Takashi Kurumaji et al., Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet. Science 365, 914-918 (2019).