Na5Co15.5Te6O36: An S=1/2 stacked Ising kagome antiferromagnet with a partially disordered ground state

S = 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 = 1/2 Ising antiferromagnet with a stacked kagome geometry, Na5Co15.5Te6O36. Upon cooling, magnetic susceptibility measurements reveal three successive magnetic transitions at T-1 = 45.2 K, T-2 = 35.4 K, and T-3 similar to 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. Na5Co15.5Te6O36 is therefore a promising candidate for S = 1/2 Ising KAFs, and this unique composite structure may shed light on the exploratory path for S = 1/2 Ising KAFs.