Emergent quasi-one-dimensional antiferromagnetism in the distorted kagome magnet CePtPb

CePtPb hosts a distorted kagome lattice of Ce³⁺ ions, providing a clean platform to investigate how reduced local symmetry and strong spin-orbit coupling reshape frustrated magnetism. Magnetization, specific heat, and magnetocaloric effect measurements, combined with a symmetry analysis of the single-ion anisotropy, demonstrate that the local m2m site symmetry selects a nearly Ising-like Kramers doublet with easy axes lying within the ab plane. This results in three distinct in-plane Ising directions and an overall easy-plane anisotropy. The low-energy magnetic response is well captured by a three-sublattice Ising model, which quantitatively reproduces the saturation magnetization for arbitrary in-plane field orientations, including [110] and [11̄0], as well as the ratio of the field-induced critical fields. For B || [110], the phase diagram exhibits two quantum critical points at B_c1 = 0.25 T and B_c2 = 0.55 T, arising from the sequential polarization of the three Ising sublattices. These results reveal that the system develops quasi-one-dimensional spin chains along the c axis, emerging from the nominally three-dimensional crystal structure composed of stacked kagome layers, and illustrate how reduced local symmetry can drive effective dimensional reduction in rare-earth Ising magnets.