Structural transition and giant spintronic response of two dimensional Manganese-Gallium $\surd $3$\times \surd $3 R30\r{ } surface structure*

In recent experiments, we have found that gallium nitride surface when exposed to transition metal atoms, results in novel well-ordered two dimensional spintronic structure, with tunable spintronic properties. A 2000 {\AA} N-polar $w$-gallium nitride (000\underline {1}) layer is grown on a sapphire substrate, by molecular beam epitaxy. The growth is monitored using reflection high energy electron diffraction system. Post growth, the standard 1$\times $1 gallium nitride surface, is exposed to sub monolayer doses of manganese. At low deposition temperature the diffraction patterns show manganese atoms forming a metastable 3$\times $3 structure, on supplying little heat to the manganese 3$\times $3 structure, it undergoes an irreversible transition to form a stable $\surd $3$\times \surd $3R30\r{ } structure. Both the structures are studied using a scanning tunneling microscope. The $\surd $3$\times \surd $3R30\r{ } structure shows a giant change in spectroscopic response on application of a very small out-of-plane magnetic field. The new findings suggest that the two dimensional magnetic nitride systems have excellent potential for both fundamental investigations and for use in future spintronic devices.