Roger Ward

Abstract:

Epitaxial Fe/MgO/Fe tunnelling magnetoresistance (TMR) structure was grown on the MgO substrate by molecular beam epitaxy, characterized in-situ by reflection high-energy electron diffraction and ex-situ by high-resolution transmission electron microscopy. The chemical states at the Fe/MgO interface have been investigated by X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there is FeO formation at interface of Fe/MgO, clearly identified by the existence of Fe2+ and Fe3+ peaks at 708.2 and 710.4eV, respectively, which locate at the high-energy side of the main metallic Fe peak. The presence of FeO layer at the Fe/MgO interface proved by XPS is likely to have considerable influence on its MR value and hence on its application in spintronics.

Abstract:

Magnetization loops for (110) ErFe2∕YFe2 multilayer films grown by molecular beam epitaxy are presented and discussed. The direction of easy magnetization for the Er layers is out of plane, near a ⟨111⟩-type crystal axis. For fields applied along the (110) crystal growth axis, out-of-plane magnetic exchange springs are set up in the magnetically soft YFe2 layers. For multilayer films that display negative coercivity at low temperatures, there is a crossover temperature above which the coercivity becomes positive, with additional transitions at high fields. These features are interpreted using micromagnetic modeling. At sufficiently high fields, applied perpendicular to the multilayer film plane, the energy is minimized by an exchange spring driven multilayer spin flop. In this state, the average magnetization of the ErFe2 layers switches into a nominally hard in-plane ⟨111⟩ axis, perpendicular to the applied field.