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Voltage control of magnetization anisotropy energy in ultrathin films

par Rosso Michel - publié le , mis à jour le

Participants : P. Allongue and F. Maroun

PhD student : Hyeonseok Sim (2022)

In this project we exploit the specificity of the electrochemical interface to investigate the influence of applied potential on the magnetic anisotropy energy (MAE) of an ultrathin layer. The electrochemical interface presents in fact a very large built-in electric field (1 V/nm) and also allows modifying the surface chemistry. We are using in situ real time magneto-optical Kerr Effect (MOKE) measurements to probe the magnetic behavior.

Figure 1 is a summary of results about electric field effect observed with as-deposited Co/Au(111) layers. For a 1.7 ML-thick film, the magnetization is out of plane. However, the shape of the magnetization curves M – H is clearly indicating that the easy axis of magnetization is tilting by 26° at -1.15 V while it is strictly out of plane at -1.6 V. This is a very large effect compared to reports of the literature. In the case the Co layers is in plane magnetized, Fig. 1b shows that the magnetic susceptibility varies linearly with the potential, which is consistent with an electric field effect. In addition, Fig. 1c demonstrates that this magneto-electric effect is a surface effect, in agreement with the screening of the electric field by the metal. Numerically the surface anisotropy energy follows the law : KSSurf = – 0.415 – 0.133 U (erg cm-2) with U in VMSE.

Figure 1 : Magneto electric effects at Co/Au(111) layers in contact with an electrolyte. The layers were grown electrochemically. (a) Influence of applied potential on magnetization curves M – H of a 1.7 ML thick layer. (b) Potential dependence of the magnetic susceptibility χ = ΔM/ΔU of in plane magnetized layers. (c) Thickness dependence of 1/χ(Δχ/ΔU).

Publications :

N. Tournerie, A. P. Engelhardt, F. Maroun, and P. Allongue, "Influence of the surface chemistry on the electric-field control of the magnetization of ultrathin films" Phys. Rev. B 86 (10), 104434 (2012).

N. Tournerie, A. Engelhardt, F. Maroun, and P. Allongue, Probing the electrochemical interface with in situ magnetic characterizations : A case study of Co/Au(111) layers, Surf. Sci. 631, 88 (2015).