Magnetic field induced reentrant multipolar ordering in the distorted kagome-lattice antiferromagnet Dy₃Ru₄Al₁₂

We report on ultrasonic and magnetocaloric-effect measurements of the hexagonal antiferromagnet Dy₃Ru₄Al₁₂ having a distorted kagome lattice. We observed a pronounced softening of the transverse modulus, C₄₄, above 30 T applied along [100], indicating an as-yet-unidentified magnetic field induced phase transition. We determined the field-temperature phase diagrams using pulsed magnetic fields up to 55.2 T, applied along [100] and [001]. Optimizing crystal-electric-field parameters within the mean-field approximation, we conclude that the enhancement of the field induced phase-transition temperature is due to electric quadrupolar and magnetic octupolar mediated interactions. We propose that the order parameter of the magnetic field induced phase transitions is the electric quadrupole O_zx, facilitated by octupole-mediated interactions.