Structural, magnetic, and anisotropic magnetocaloric properties in antiferromagnetic compounds MBaYb(BO3)2 (M = K, Na)

In this study, high-quality single crystals of MBaYb(BO₃)₂ (where M = K, Na) were successfully grown using the self-flux technique. The structural, anisotropic magnetic, and magnetocaloric properties of KBaYb(BO₃)₂ and NaBaYb(BO₃)₂ were comprehensively studied through X-ray diffraction (XRD), isothermal magnetization, anisotropy susceptibility response, and specific heat tests. The powder X-ray diffraction scan of the crushed as-grown crystal confirms that both compounds crystallize in a trigonal symmetry, classified under the Rm (no. 166) space group, but they exhibit distinct structural arrangements. The temperature-dependent anisotropic susceptibility and specific heat data for KBaYb(BO₃)₂ and NaBaYb(BO₃)₂ show no evidence of long-range magnetic ordering down to 2 K, suggesting paramagnetic behavior in the low-temperature regime. Furthermore, using Maxwell's equations, the calculated magnetic entropy change (−ΔS_m) attains a highest value of 7.7 J mol⁻¹ K⁻¹ for KBaYb(BO₃)₂ with a change in applied field from 0 to 7 T at 2 K, while for NaBaYb(BO₃)₂ it is 7.0 J mol⁻¹ K⁻¹. Additionally, KBaYb(BO₃)₂ exhibits an adiabatic temperature change (−ΔT_ad) of 3.4 K, compared to 1.6 K for NaBaYb(BO₃)₂, under a field change from 0 to 7 T. The MBaYb(BO₃)₂ (where M = K, Na) could be strong candidates for magnetic coolant in the cryogenic temperature range, as indicated by a notable magnetic entropy change in the magnetocaloric effect (MCE) parameters, which is comparable to or even exceeds that of well-known magnetic refrigerants.