Electrochemistry-mediated voltage control of magnetization close to ON/OFF switching is realized in electrodeposited oxide/metal nanoislands.

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Electric field control of magnetization and anisotropy in layered structures with perpendicular magnetic anisotropy is expected to increase the versatility of spintronic devices. As a model system for reversible voltage induced changes of magnetism by magnetoionic effects, we present several oxide/metal heterostructures polarized in an electrolyte. Room temperature magnetization of Fe-O/Fe layers can be changed by 64% when applying only a few volts in 1M KOH. In a next step, the bottom interface of the in-plane magnetized Fe layer is functionalized by an L10 FePt(001) underlayer exhibiting perpendicular magnetic anisotropy. During subsequent electrocrystallization and electrooxidation, well defined epitaxial Fe3O4/Fe/FePt heterostructures evolve. The application of different voltages leads to a thickness change of the Fe layer sandwiched between Fe-O and FePt. At the point of transition between rigid magnet and exchange spring magnet regime for the Fe/FePt bilayer, this induces a large variation of magnetic anisotropy.

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The electrode reactions during the initial stages of Fe electrodeposition on GaAs from a sulfate-based aqueous electrolyte, were investigated. Electrochemical quartz microbalance measurements were carried out to distinguish hydrogen evolution from Fe deposition. For conditions with a lower hydrogen evolution rate, hemispherical Fe nanoparticles with negligible in-plane magnetic anisotropy are obtained. In contrast, when hydrogen evolution dominates over Fe electrodeposition, the deposited nanoparticles exhibit a defined faceted shape, crystallographic alignment and magnetic in-plane anisotropy. This beneficial impact of hydrogen evolution on the epitaxy is discussed with regard to the role of hydrogen adsorption during Fe/GaAs interface formation.

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