The controlled growth of magnetic thin films on gallium nitride substrates may lead to multifunctional spintronic devices
Thin films of MnGa and GaAs doped with Mn atoms are being widely studied for fabricating spintronic devices. Such materials are usually deposited on GaAs substrates by molecular beam epitaxy — a process where evaporated atoms condense on a surface and can react with one another. The growth of MnGa on GaN substrates has proved to be difficult, however, because Mn and Ga form non-crystalline phases that do not exhibit the sort of magnetic properties necessary for spintronic applications.
Now, Erdong Lu and colleagues1 of Ohio University and Ohio State University in the USA have successfully deposited crystalline MnGa thin films on GaN substrates. Using a molecular-beam epitaxy system fitted with a nitrogen plasma source, high-quality films can be grown in which the ratio of Mn to Ga can be carefully controlled. Film growth was monitored by scanning tunnelling microscopy and a high-energy electron diffraction technique.
Significantly, the magnetic moments of the films depend on their composition and structure, which can be varied by altering the flux of either the Mn or Ga atoms. This discovery offers an additional degree of freedom in the design and construction of optical spintronic devices operating at short wavelengths.
Lu, E. et al. Phys. Rev. Lett. (2006). 10.1103/PhysRevLett.97.146101