$S=\frac{1}{2}$ Ising kagome antiferromagnets (KAFs) are rare in reality. In this paper, we report the magnetic ground state and field-induced transitions of an $S=\frac{1}{2}$ Ising antiferromagnet with a stacked kagome geometry, ${\mathrm{Na}}_5{\mathrm{Co}}_{15.5}{\mathrm{Te}}_6{\mathrm{O}}_{36}$. Upon cooling, magnetic susceptibility measurements reveal three successive magnetic transitions at $T_1$ = 45.2 K, $T_2$ = 35.4 K, and $T_3\sim$ 20 K. When the magnetic field is applied along the Ising $c$ axis, a strikingly anomalous initial magnetization lying outside the hysteresis loop is observed below $T_3$. Through detailed characterizations, the magnetic field vs temperature phase diagram is established. A partially disordered antiferromagnetic state is proposed below $T_1$, which becomes frozen below $T_3$. ${\mathrm{Na}}_5{\mathrm{Co}}_{15.5}{\mathrm{Te}}_6{\mathrm{O}}_{36}$ is therefore a promising candidate for $S=\frac{1}{2}$ Ising KAFs, and this unique composite structure may shed light on the exploratory path for $S=\frac{1}{2}$ Ising KAFs.

• Received 7 December 2021
• Accepted 29 March 2022

DOI:https://doi.org/10.1103/PhysRevB.105.144406