Magnetic phase diagram and crystal-field effects in the kagome-lattice antiferromagnet U3Ru4Al12

We report on the magnetic phase diagram of the distorted kagome-lattice antiferromagnet ${\mathrm{U}}₃{\mathrm{Ru}}₄{\mathrm{Al}}₁₂$ determined through measurements of magnetic and elastic properties. For field applied along the [100] and [120] axes of the hexagonal crystal structure, we find pronounced anomalies in the magnetization and elastic moduli that signal the existence of unknown magnetic phases. Our crystal-electric-field (CEF) analysis evidences interlevel quadrupolar interactions between the ground-state singlet and the first excited doublet. These interactions lead to a large softening of the shear elastic modulus ${C}₄₄$. The large number of phases and pronounced elastic softening suggest that geometric frustrations and CEF effects play an important role in the physical properties of ${\mathrm{U}}₃{\mathrm{Ru}}₄{\mathrm{Al}}₁₂$.