Probe the magnetic ground state and quantum phase transition in a novel triangular-lattice dipolar antiferromagnet KBaGd(BO3)2

Triangular-lattice antiferromagnets (TLAF) serve as a fertile playground for the exploration of exotic quantum states with the help of geometrical frustration, for example, possible quantum spin liquid (QSL). Although the realization of QSL in real materials is still controversial, researchers have already benefited from the TLAFs for their large magnetocaloric effect due to the huge frustration-induced low-temperature magnetic entropy. KBaGd(BO3)2 (KBGB) with the S=7/2 Gd3+ ions forming a perfect triangular lattice is expected to offer a much larger entropy change upon cooling and accordingly a pronounced magnetocaloric effect, thus holding great potential in the area of ultra-low-temperature magnetic refrigeration. This is already well confirmed in our magnetocaloric measurement on single-crystal samples of KBGB. Starting from an initial environmental temperature of 2 K, it reaches an extremely low temperature of around 90 mK by demagnetization using a field of 6 T. The magnetic ground state of KBGB, however, is largely unknown. In addition, a field-induced quantum phase transition (QPT) is observed around Hc = 0.77 T in the magnetocaloric measurements for a field applied along the c axis (H//c). Here we propose to perform zero-field (ZF) and longitudinal-field (LF) μSR measurements on KBGB, to figure out its magnetic ground state and the nature of the QPT, which is of great importance for understanding its extraordinary performance in the magnetic refrigeration.