Quantum-limit phenomena in rare-earth-based layered EuZn₂As₂ and CsNdSe₂

Layered EuZn₂As₂ and CsNdSe₂ are candidate magnetic topological materials with the magnetism from the involved rare-earth elements. While Eu forms a square lattice with its moment orders antiferromagnetically below 19 K in EuZn₂As₂, Nd in CsNdSe₂ forms a triangular lattice thus never orders magnetically down to 0.04 K. By applying pulsed magnetic fields up to 60 T, spin reorientation is observed accompanied with giant magnetoresistance (MR) in EuZn₂As₂. After passing the first Landau level, the large linear MR occurs at high fields corresponding to the quantum limit. On the other hand, the application of the magnetic field leads to long-range magnetic ordering with the highest transition temperature at 0.3 K in CsNdSe₂, implying the quantum spin liquid ground state at the ambient condition. Our findings help understand the intimate relationship between magnetism and electronic topology in magnetic topological materials.