Visualizing Weak Ferromagnetic Domains In Multiferroic Hexagonal Ferrite Thin Film

We report cryogenic magnetic force microscopy (MFM) studies of a 200-nm-thick hexagonal (h) LuFeO3 film grown by molecular-beam epitaxy on a (111)-oriented yttria-stabilized cubic-zirconia substrate. Labyrinthlike domains similar to 1.8 mu m in size were observed after zero-field cooling below the Neel temperature, T-N approximate to 147 K, where weak ferromagnetic order (P6(3)(cm) under bar) with a canted moment of M-S approximate to 0.02 mu(B)/f.u. exists. At 6 K, MFM images of the magnetization reversal process reveal a typical domain behavior of a pinning-dominated hard magnet. The pinning strength is substantially reduced at elevated temperature. The temperature dependence of the domain contrast demonstrates that our MFM is able to detect the domain contrast of magnets with tiny magnetic moments (similar to 0.002 mu(B)/f.u.). An upper limit of the linear magnetoelectric coefficient of h-LuFeO3 (alpha(zz) < 6 ps/m) is estimated by magnetoelectric force microscopy measurements.