Determining the coercivity of anisotropic Heisenberg magnets by Monte Carlo sampling: Application to the design of permanent magnets

Monte Carlo methods are widely used to study magnetism. However, their use to the calculation of coercivity has been problematic because of difficulties in quantifying Monte Carlo time. Here we propose a new approach of studying coercivity based on Monte Carlo sampling of the switching time at different reverse fields. This method allows comparative analysis of how coercivity is affected by various factors without needing time quantification of the Monte Carlo step. We apply the new method to study antiferromagnet-ferromagnet exchange coupling systems and show that practically large coercivity and enhanced maximum energy product can be achieved by properly adding antiferromagnet to high-magnetization ferromagnets such as Fe₁₆N₂. The finding is important to the design of new rare-earth-free permanent magnets.