Investigation on the formation process of single-crystalline GaOx barrier in Fe/GaOx/MgO/Fe magnetic tunnel junctions

We have grown Fe(0 0 1)/GaOx(0 0 1)/MgO(0 0 1)/Fe(0 0 1) magnetic tunnel junctions (MTJs) with or without in situ annealing after the deposition of GaOx layer and performed structural characterizations by focusing on the formation process of the single-crystalline GaOx. It was found that, even without the in situ annealing, the as-grown GaOx grown on the MgO was mostly single-crystalline except near the surface region (amorphous). The crystallization temperature of the amorphous region was reduced from 500 °C down to 250 °C by depositing the Fe upper electrode (poly-crystalline). It was clarified that the crystallization of the amorphous region near the Fe/GaOx interface caused the realignments of the crystal grains in the poly-crystalline Fe upper electrode, and, as a result, the fully epitaxial Fe/GaOx/MgO/Fe structure is eventually formed. All the MTJs showed high tunneling magnetoresistance ratios (about 100%) at room temperature, which was almost independent of the formation temperature of the single-crystalline GaOx.