Bi2YbO4Cl: A two-dimensional square-lattice compound with Jeff=21 magnetic moments

The interplay between the quantum effects from low -dimensionality and the spin -orbit coupling leads to exotic ground states with unusual excitations. We report the structural, magnetic, heat capacity, and electronic structure studies of Bi2YbO4Cl, which constitutes a structurally perfect 2D square lattice with rare-earth magnetic Yb3+ ions. The magnetization and heat capacity data analysis confirms that the Yb3+ ion hosts the spin -orbit driven Jeff = 12 state at low temperatures. From the fit to the Curie -Weiss law on the magnetic susceptibility data in the low -temperature region, the observed Curie -Weiss temperature is about -1 K, implying an antiferromagnetic (AFM) coupling between the Yb3+ moments. The heat capacity data show the presence of a broad maximum at 0.3 K and the absence of any sharp magnetic anomaly down to 0.09 K, indicating the onset of short-range correlations. Our first -principles calculations based on density functional theory provide further insight into the role of the microscopic parameters. In particular, it points out the crucial role of spin -orbit coupling in driving both the Jeff = 12 state as well as the antiferromagnetic interaction between the nearest -neighbor Yb3+ moments that is consistent with experimental results. The total energy calculations suggest an easy -axis (out -of -plane) anisotropy of the spins.