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Electric Quadrupolar Contributions in the Magnetic Phases of UNi4B

Yanagisawa, T.; Matsumori, H.; Saito, H.; Hidaka, H.; Amitsuka, H.; Nakamura, S.; Awaji, S.; Gorbunov, D.; Zherlitsyn, S.; Wosnitza, J.; Uhlirova, K.; Valiska, M.; Sechovsky, V.

We present acoustic signatures of the electric quadrupolar degrees of freedom in the honeycomb-layer compound UNi4B. The transverse ultrasonic mode C66 shows softening below 30 K both in the paramagnetic phase and antiferromagnetic phases down to ∼0.33 K. Furthermore, we traced magnetic field-temperature phase diagrams up to 30 T and observed a highly anisotropic elastic response within the honeycomb layer. These observations strongly suggest that Γ6 (E2g) electric quadrupolar degrees of freedom in localized 5f2 (J = 4) states are playing an important role in the magnetic toroidal dipole order and magnetic-field-induced phases of UNi4B, and evidence some of the U ions remain in the paramagnetic state even if the system undergoes magnetic toroidal ordering.

Publ.-Id: 32522