Growth and Properties of Mn$_{\mathrm{x}}$Ga Magnetic Nanostructures

Rare-Earth (RE) magnets are becoming more expensive and less available for current applications in technology. Mn$_{\mathrm{x}}$Ga (x$=$2-3) has previously shown coercivity of \textgreater\ 2.5 T, close to that of RE magnets.\footnote{T.J. Nummy, S.P Bennett, T. Cardinal, and D. Heiman, \textit{Large Coercivity in Nanostructured Rare-earth-free Mn}$_{x}$\textit{Ga Films}, Appl. Phys. Lett. \textbf{99}, 252506 (2011).} In this project, the vapor-liquid-solid (VLS) method was used to grow nanoparticles of Mn$_{\mathrm{x}}$Ga (x$=$1-3) with MBE. The goal was to study the magnetic properties as a function of reduced dimensionality. The samples were prepared by depositing a 3-6 nm layer of Au on Si, GaAs, and glass. It was found that the miscibility of Ga and Au is high, but for Mn and Au it is much lower. Therefore, during the growth process Ga was deposited on the gold catalyst followed by Mn deposition. The samples were then annealed at temperatures 100-500 $^{\circ}$C. Nanostructures, including regions of nanowires, were found using scanning electron microscopy on all samples. The magnetic properties of the nanostructured samples were studied with SQUID magnetometry and found to have a magnetization of 200 emu/cm$^{3}$.