  We predict that cubic MN4 (M=Mn, Fe, Co) are all half metals with the largest
spin gap up to ~ 5 eV. They possess robust ferromagnetic ground states with the
highest Curie temperature up to ~ 103 K. Our calculations indicate these
compounds are energetically favored, dynamically and mechanically stable. It is
proposed that self-doping of these 3d transition metals occurs in MN4 due to
the reduction in electronegativity of N2 dimers. This model can well explain
the calculated integer magnetic moments, large spin gaps of MN4 and
semiconducting behavior for NiN4 as well. Our results highlight the difference
in electronegativity between transition metal ions and non-metal entities in
forming half metals and the role of N2 dimer in enlarging the spin gaps for
nitride half metals.
