Diluted ferromagnetic semiconductors offer great opportunities for the integration of ferromagnetism and semiconductor band structure engineering to manipulate both electron spin and charge in spintronics. Furthermore, Mn-doped GaN is of great interest since its Curie temperature is predicted to be over 300 K. However, while it is generally accepted that the ferromagnetism observed in GaMnAs is carrier-mediated, for Mn-doped nitrides the origin of ferromagnetism and the coupling between the magnetic element and host still remain controversial.
Using XAS and XMCD, we have investigated the Mn local structure, magnetism, and Ga moments in molecular beam epitaxy (MBE) grown Mn-doped GaN films. We find two distinct Mn sites and a Ga moment antiparallel to Mn. First-principles calculations reproduce this phenomenology and indicate that Mn preferentially populates Ga sites neighboring N-split-interstitial defects. These results show that defects may strongly affect the Mn ordering and consequently magnetism, and that the GaN valence band is polarized, providing a long-range ferromagnetic ordering mechanism for GaMnN.
Published in Physical Review Letters:
“Role of Defect Sites and Ga Polarization in the Magnetism of Mn-Doped GaN“, D. J. Keaney, S. H. Cheung, S. T. King, M. Weinert, and L. Li, Phys. Rev. Lett. 95, 257201 (2005).