Magnetic phases of the frustrated ferromagnetic spin-trimer system Gd3Ru4Al12 with a distorted kagome lattice structure

Magnetization and specific heat measurements were conducted on single-crystalline Gd3Ru4Al12, in which magnetic Gd-Al layers with a distorted Kagome lattice structure and nonmagnetic Ru-Al layers are stacked alternately along the c axis. A previous study indicated that the distorted Kagome lattice structure of Gd-Al layers effectively translates into an antiferromagnetic (AFM) triangular lattice in association with ferromagnetic (FM) spin trimerization at low temperatures. The present results indicate that the spin system of Gd3Ru4Al12 has two types of anisotropies: easy-plane-type and easy-axis-type anisotropies. The trimers carry magnetic quadrupole moments when the FM directivity of the component spins is imperfect. The origin of the unusual magnetic anisotropies that were observed can be explained by the magnetic quadrupole interactions that take place between the trimers. The stability of a helical structure in the crystal with inversion-symmetry is discussed.