Antiferromagnetic ordering and critical behavior induced giant magnetocaloric effect in distorted kagome lattice Gd${}_3$BWO${}_9$

Abstract

We synthesize the high-quality Gd${}_3$BWO${}_9$ single crystal and investigate its lowtemperature magnetic and thermodynamic properties. Below $T{}_{\mathrm{N}}$ = 1.08 K, the anisotropic behavior of magnetic susceptibilities reveals that the Gd${}^{3+}$ moments exhibit the dominant antiferromagnetic coupling along the $c$-axis, while displaying a ferromagnetic arrangement in kagome plane. With pronounced magnetic frustration, in adiabatic demagnetization refrigeration experiments starting from initial conditions of 9 T and 2 K, Gd${}_3$BWO${}_9$ polycrystal reaches a minimum temperature of 0.151 K, significantly lower than its $T{}_{\mathrm{N}}$. Due to the high density of Gd${}^{3+}$ ions ($S$=7/2), the maximum magnetic entropy change reaches over 50 J kg${}^{-1}$ K${}^{-1}$ under fields up to 7 T in Gd${}_3$BWO${}_9$, nearly 1.5 times as large as commercial sub-Kelvin magnetic coolant Gd${}_3$Ga${}_5$O${}_{12}$(GGG). The H-T phase diagram of Gd${}_3$BWO${}_9$ under $H$//$c$ exhibits field-induced critical behavior near the phase boundaries. This observation aligns with the theoretical scenario in which a quantum critical point acts as the endpoint of a line of classical second-order phase transitions. Such behavior suggests the importance of further investigations into the divergence of magnetic Grüneisen parameter in the vicinity of critical field at ultralow temperatures.

This manuscript contains 5 figures, to appear in Phys. Rev. Mater soon

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