Magnetism in The Square Lattice Compounds YbBi₂IO₄ and YbBi₂ClO₄

The square lattice affords a simple platform to study quantum effects in two-dimensions (2D). This is because a two-interaction square lattice system is frustrated when the interactions are antiferromagnetic, with the phase diagram including the quantum spin liquid state. YbBi₂IO₄ and YbBi₂ClO₄ possess well-isolated layers containing square lattices of Yb³⁺ and are thus good candidates for realizing quantum effects on a square lattice. Here, we examine the magnetism and crystal field levels in the title compounds through a combination of specific heat, magnetization and inelastic neutron scattering measurements on polycrystalline samples. The results reveal that these materials host well-isolated Kramer’s doublet ground states, with quasi-2D magnetic behavior as well as evidence for magnetic frustration. YbBi₂IO₄ and YbBi₂ClO₄ are therefore interesting candidates for future studies of 2D quantum magnetism.