Growth and characterization of half-Heusler half-metal candidate CoTi$_{1-x}$Fe$_{x}$Sb*

Recent predictions suggest the semiconducting half-Heusler compound, CoTiSb, exhibits half-metallicity when substitutionally alloyed with Fe. However, to date, few studies have examined the growth of high-quality single crystal thin films of Fe doped CoTiSb. Here, we report the epitaxial growth of the substitutionally alloyed half-Heusler series CoTi$_{1-x}$Fe$_{x}$Sb by molecular beam epitaxy and the influence of Fe on the structural, electronic, and magnetic properties. CoTi$_{1-x}$Fe$_{x}$Sb epitaxial films are grown on InAlAs (001) grown on InP (001) substrates for concentrations 0$\le $x$\le $1. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and XRD. For higher Fe content films a lower growth temperature is necessary to minimize interfacial reactions. Using \textit{in-situ} XPS, only small changes in the valence band are detected for Fe x$\le $0.15. Temperature dependent transport reveals thermally activated behavior for x$\le $0.5. Ferromagnetism is observed in SQUID magnetometry with a Curie temperature \textgreater 400K and a saturation magnetization of 3.4 $\mu $B/Fe atom formula unit. Ferromagnetic resonance indicates a transition from weak to strong interaction and homogeneity as Fe content is increased.