Canted antiferromagnetism in a spin-orbit coupled S_eff = 3/2 triangular-lattice magnet DyAuGe

The exploration of nontrivial magnetic states induced by strong spin-orbit interaction is a central topic of frustrated magnetism. Numerous studies have been conducted on rare-earth-based magnets and 4d/5d transition metal compounds. These are mostly described by an effective spin S_eff  = 1/2 for the Kramers doublet of the lowest crystal-electric-field levels. The variety of magnetic orderings can be greatly enhanced when magnetic dipolar moments intertwined with multipolar degrees of freedom, which are described by higher-rank tensors and often require the magnetic ions to have S_eff  > 1/2. Here, using synchrotron x-ray diffraction near the Dy L₃ edge, we unveil a canted antiferromagnetic ground state arising from a quasi-quartet (S_eff  =  3/2) of 4f electrons in a triangular-lattice (TL) rare-earth intermetallics DyAuGe. The magnetic moment and electric-quadrupole moment are closely interlocked and a noncollinear magnetic-dipole alignment is induced by antiferroic electric-quadrupole (AFQ) ordering in the TL layers. The AFQ order is suppressed by an in-plane magnetic field, leading to the metamagnetic transition to a collinear up-up-down magnetic state. These findings offer insights into the emergence of nontrivial magnetic states in frustrated TL systems with S_eff > 1/2.