Epitaxial Growth of Binary Ferromagnetic Mn$_{3-\delta}$Ga Thin Films on Wurtzite GaN(0001) and Investigation by Atomic Scale Scanning Tunneling Microscopy

Due to increasing interest in developing new magneto-optical and magneto-electronic devices, and spin injection sources in spintronics applications, ferromagnetic (FM){$\backslash$MnxGay} is an attractive candidate system to explore. Here we report that binary FM {Mn$_{3-\delta}$Ga}(1.14$<$$\delta$$<$2.0) single crystalline thin films has been epitaxially grown on ({\it w})-GaN(0001)surfaces using molecular beam epitaxy. The face-centered tetragonal structure of {Mn$_{3-\delta}$Ga} thin films with CuAu-L1$_{0}$ type ordering has been determined $\textit{in situ}$ by both reflection high energy electron diffraction and atomic-scale scanning tunneling microscopy. The epitaxial relationship of the {Mn$_{3-\delta}$Ga} with GaN(0001) is (111)[1$\bar{1}$0]$_{MnGa}$ $\parallel$ (0001)[1$\bar{1}$00]$_{GaN}$ and (111)[11$\bar{2}$]$_{MnGa}$ $\parallel$ (0001)[11$\bar{2}$0]$_{GaN}$. The hysteresis loops of the thin films show magnetic anisotropy along \textit{in-plane} and \textit{out-of-plane} directions. It is found that Curie temperature and magnetic moments of the {Mn$_{3-\delta}$Ga} thin films are closely related to the Mn content, and the reconstruction changes from {1$\times$1} to {2$\times$2} by increasing the ratio of Mn to Ga during the growth. Thus, we have achieved reconstruction-control of magnetic properties.