Transition from an incommensurate spin density wave to a commensurate magnetic order in a triangular lattice compound Ho2PdAl6Ge4

Abstract

Rare-earth (RE) intermetallics on a triangular lattice are promising candidates for generating interesting magnetic phases due to the complex interplay between Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction and geometrical frustration. Here we report the exotic magnetic structure of a layered compound Ho2PdAl6Ge4 with triangular lanthanide nets. Magnetization and heat capacity measurements in zero magnetic field reveal two magnetic phase transitions at TN1 = 10.8 K and TN2 = 6.0 K. Neutron powder diffraction demonstrates a commensurate antiferromagnetic phase with k1 = (0, 0, 1.5) below TN2. With increasing temperature, another incommensurate vector appears and therefore, the magnetic structure of the intermediate state is identified as an unusual incommensurate spin density wave with two propagation vectors k1 = (0, 0, 1.5) and k2 = (0.0492, 0.0492, 1.5). The magnetic moments in the intermediate state rotate continuously and form an unusual S-shaped wave arrangement in the ab plane, sharing similarities with typical cycloid and helix magnetic orders. These results identify Ho2PdAl6Ge4 as a candidate for exploring field-induced topological magnetic phases such as skyrmions, opening the way for further investigations on the family of RE2PdAl6Ge4 materials.