  The magnetism in 12.5% and 25% Mn delta-doped cubic GaN has been investigated
using the density-functional theory calculations. The results show that the
single-layer delta-doping and half-delta-doping structures show robust ground
state half-metallic ferromagnetism (HMF), and the double-layer delta-doping
structure shows robust ground state antiferromagnetism (AFM) with large
spin-flip energy of 479.0 meV per Mn-Mn pair. The delta-doping structures show
enhanced two-dimensional magnetism. We discuss the origin of the HMF using a
simple crystal field model. Finally, we discuss the antiferromagnet/ferromagnet
heterostructure based on Mn doped GaN.
