Magnetic properties of 2D Chromium trihalides by first-principles calculations

This thesis investigates the magnetic properties of the chromium trihalides series CrX3 with X = Cl, Br, I at both the bulk and monolayer limits, with a particular focus on the effect of low-dimensionality and spin-orbit coupling. Combining the four-states method with very accurate total energy calculations based on density functional theory, we have systematically targeted the isotropic and anisotropic contributions to the exchange interactions within these materials. Our findings reveal that they are significantly enhanced by the spin-orbit coupling of the associated halide atoms. To further understand the behaviour of the monolayers at finite temperatures, we initialized a quadratic spin Hamiltonian with the so obtained exchange couplings and consequently performed Monte Carlo simulations. The results indicate a substantial overestimation of the Curie temperatures for the monolayers. We finally suggest a reasonable explanation of the reported discrepancy, but that is still an open question as it would require further tests to be eventually confirmed.