Calculations based on density-functional theory show that the stability and magnetic properties of small Mn clusters can be fundamentally altered by the presence of nitrogen. Not only are their binding energies substantially enhanced, but also the coupling between the magnetic moments at Mn sites remains ferromagnetic irrespective of their size or shape. In addition, these nitrogen-doped Mn clusters carry giant magnetic moments ranging from $4{\mu }_{\mathrm{B}}$ in MnN to $22{\mu }_{\mathrm{B}}$ in $\mathrm{M}{\mathrm{n}}_{\mathrm{5}}\mathrm{N}$. It is suggested that the giant magnetic moments of ${\mathrm{M}\mathrm{n}}_x\mathrm{N}$ clusters may play a key role in the ferromagnetism of Mn-doped GaN which exhibit a wide range (10–940 K) of Curie temperatures.

• Received 24 April 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.185504