CEF excitations in a triangular-lattice antiferromagnet Rb3Er(PO4)2

Rb Er(PO ) represents a new frustrated system with an ideal triangular lattice of Er ions. Our ac susceptibility and specific heat measurements reveal two successive magnetic transitions at T1 = 0.12 K and T2 = 0.25 K under zero field. With a field of 0.1 T, the T1 transition disappears and T2 shifts to a higher temperature, suggesting potential ferromagnetic behavior. At 0.7 T, all magnetic transitions vanish, and the system enters a possible quantum disordered state. With further increasing fields, the system undergoes a field-induced first-order-like long-range magnetic ordering at around 7 T, displaying a rich phase diagram. For a better understanding of these intriguing magnetic properties, we propose to measure the CEF excitations in Rb3Er(PO4)2.