Robust magnetism and phase transitions in ultrathin ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ flakes

Competing spin-orbit coupling, electron correlation, and structural distortion are crucial factors influencing the physics of oxides, including iridates. We investigate ultrathin chemically bonded layered ${\mathrm{Na}}_2{\mathrm{IrO}}_3$, which exhibits characteristics of a proximate quantum spin liquid in its bulk form. Employing first-principles calculations, we explore the interplay between Heisenberg and Kitaev interactions within the two-dimensional limit. Contrary to the conventional understanding of van der Waals materials, magnetism in ultrathin ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ is reinforced in the two-dimensional limit. As the zigzag antiferromagnetic state stabilizes, it diverges further from the Kitaev spin-liquid state due to enhanced Heisenberg and off-diagonal exchange interactions. Furthermore, carrier doping can tune the electronic and magnetic states, resulting in combined Mott insulator-to-metal and antiferromagnetic-to-ferromagnetic transitions. These findings provide compelling insights into the magnetism of a two-dimensional realm in non-van der Waals correlated oxide flakes.