Properties of LuFe$_{2}$O$_{4}$ Films Grown by Molecular-Beam Epitaxy

LuFe$_{2}$O$_{4}$ is an exotic material with a simultaneous existence of ferroelectricity and ferrimagnetism at the highest temperature (240 K) of any known material [1]. 25 nm thick films of this unusual multiferroic were grown by MBE on MgAl$_{2}$O$_{4}$, MgO, and SiC substrates. XRD shows that the LuFe$_{2}$O$_{4}$ films are single-phase and epitaxial. Film stoichiometry was regulated using an adsorption controlled growth process by depositing LuFe$_{2}$O$_{4}$ in an iron rich environment at pressures and temperatures where the excess iron desorbs from the film surface during growth. STEM images reveal the layered structure of LuFe$_{2}$O$_{4}$ and a clean substrate-film interface free of second phases. The magnetization data exhibits a rapid increase in magnetization below 240 K consistent with the bulk paramagnetic to ferrimagnetic phase transition. On further cooling, the zero field cooled (ZFC) branch of the magnetization displays a peak at 205 K that is suggestive of a glassy transition, which is also seen in bulk samples. At 100 K and 70 kOe, we observe a saturation magnetization of 2.4 $\mu _{B}$/ f. u. (theoretical value of 3 $\mu _{B}$/ f. u.) \\[4pt] [1] Ikeda \textit{et. al}., Nature \textbf{436} (2005) 1136--1138.