Motivated by intriguing properties of geometrically frustrated systems, in the present work, another member of the triple perovskite family, ${\mathrm{Ca}}_3{\mathrm{CoSb}}_2{\mathrm{O}}_9$, with a ${\text{Co}}^{2+}$ triangular motif, has been synthesized, and its structural, magnetic, and thermal transport properties were studied in detail. The triple perovskite crystallizes in the monoclinic phase with a $P{2}_1/c1$ symmetry. A cusp in the dc magnetic susceptibility, accompanied by a $\lambda$-like feature in the ac susceptibility and specific heat, indicates a transition to an antiferromagnetic state below $T_N\sim 3.8\text{K}$. Magnetic susceptibility measurements confirm the existence of the ${\mathrm{Co}}^{2+}$ moments with $S=1/2$ spin state, a large Curie-Weiss temperature of ${\theta }_{\text{CW}}=-76.70\text{K}$, and a significant degree of magnetic frustration ($f=|{\theta }_{\text{CW}}/T_N|\approx 20$). The temperature-dependent ac magnetization reveal a prominent peak at $T_N$ that exhibits characteristic magnitude suppression and a subtle shift (3.8 to 4.1 K) with increasing frequency from 0.21 to 631 Hz. Additionally, a nondispersive kink at $T\sim 7.0\text{K}$ was observed, indicative of persistent short-range magnetic correlation above $T_N$. Moreover, the absence of a spin-flop transition or a $M_s/3$ magnetization plateau in field-dependent studies up to $16\text{T}$, suggests that the structural distortions in ${\text{Ca}}_3{\text{CoSb}}_2{\text{O}}_9$ stabilize a noncollinear ${120}^{\circ }$ spin structure against field-induced quantum phase transitions.

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• Frustrated magnetism
• Triangular lattice
• Magnetization measurements
• Magnetotransport
• Sintering
• X-ray diffraction
• X-ray photoelectron spectroscopy