Adiabatic Demagnetization Cooling Well below the Magnetic Ordering Temperature in the Triangular Antiferromagnet KBaGd(BO3)2

Crystal structure, thermodynamic properties, and adiabatic demagnetization refrigeration (ADR) effect in the spin-7/2 triangular antiferromagnet KBaGd(BO3)2 are reported. With the average nearest-neighbor exchange coupling of 44 mK, this compound shows magnetic order below T_N = 263 mK in zero field. The ADR tests reach the temperature of T_min = 122 mK, more than twice lower than T_N, along with the entropy storage capacity of 192 mJK^-1cm^-3 and the hold time of more than 8 hours in the PPMS setup, both significantly improved compared to the spin-1/2 Yb^3+ analog. We argue that KBaGd(BO3)2 shows a balanced interplay of exchange and dipolar couplings that together with structural randomness and geometrical frustration shift T_min to well below the ordering temperature T_N, therefore facilitating the cooling.