Ab initiocalculation of the magnetic Gibbs free energy of materials using magnetically constrained supercells

Complex magnetic phases are exploited in many important solid-state technologies, but their first-principles modeling at finite temperature is a major challenge. The authors present an approach to the $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ description of temperature-dependent noncollinear magnetic structures, based on supercell calculations. It generalizes an approximate method to compute the magnetic Gibbs free energies of disordered local moments to more accurate density functional theory codes. The application uncovers structural and electronic mechanisms of discontinuous transitions to magnetic phases with technological functionality.