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Abstract:
In this work, we employ and critically evaluate a first-principles approach based on supercell calculations for predicting the magnetic critical order-disorder temperature Tc. As a model material we use the recently discovered nanolaminate Mn2GaC. First, we derive the exchange interaction parameters Jij between pairs of Mn atoms on sites i and j of the bilinear Heisenberg Hamiltonian using the novel magnetic direct cluster averaging method (MDCA), and then compare the J′s from the MDCA calculations to the same parameters calculated using the Connolly-Williams method. We show that the two methods yield closely matching results, but observe that the MDCA method is computationally less effective when applied to highly ordered phases such as Mn2GaC. Secondly, Monte Carlo simulations are used to derive the magnetic energy, specific heat, and Tc. For Mn2GaC, we find Tc=660K. The uncertainty in the calculated Tc caused by possible uncertainties in the J′s is discussed and exemplified in our case by an analysis of the impact of the statistical uncertainties of the MDCA-derived J′s, resulting in a Tc distribution with a standard deviation of 133 K. © 2016 American Physical Society.
