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 ${\mathrm{U}}_3{\mathrm{Ru}}_4{\mathrm{Al}}_{12}$.

• Received 25 November 2018

DOI:https://doi.org/10.1103/PhysRevB.99.054413