Heusler alloys with Mn and Co have been found to exhibit interesting electronic and magnetic properties. Mn 2 CoAl is well known SGS compound while Mn 2 CoGa has weak half metallic character. By using plane wave pseudo-potential method, we studied the effect of Fe and Cr doping on half-metalicity and magnetism of these compounds. The doping destroys the SGS nature of Mn 2 CoAl while the small-scale doping enhance the half-metallicity of Mn 2 CoGa making it perfect half-metal. In case of Mn 2 CoAl, the doping decrease the band gap while increase in band width is noticed for Mn 2 CoGa. The half-metallicity is destroyed in both cases when the doping level is beyond certain degree. Moreover, we have also computed magnetic behavior of Mn 2 CoZ alloys and we found that total magnetic moments of dopped samples have higher values than that of pristine compounds.

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