Abstract
Stoichiometric and ordered hexagonal phase of MnBi are difficult to obtain due to the peritectic reaction of the materials constituents. Thus, inter-site mixing of Mn and Bi is expected. Given that the material is a promising rare-earth free permanent magnet, we study the effects of inter-site chemical disorder on its magnetic properties, using ab initio density functional based electronic structure methods. Our calculations, focusing on inter-site substitutional disorder, show that excess of Mn and Bi ions in MnBi have detrimental effects on its magnetic properties. We find that inter-site chemical disorder not only decreases the total magnetization, but also reduces the materials׳ ferromagnetic transition temperature. The latter is deduced from the calculated magnetic pair-exchange parameters by means of linear response technique. Our calculations suggest that the inter-site disorder of Mn and Bi ions in MnBi must be minimized for its optimum performance in permanent magnet applications.
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