Magnetoelectric effect in metallic nanostructures : ab-initio electron theory and atomistic modelling

Der magnetoelektrische Effekt in metallischen Nanostrukturen wird untersucht. Dabei wird die Veränderung der magnetokristallinen Oberflächenanisotropieenergie dünner Metallfilme als Funktion externer elektrischer Felder im Rahmen der elektronischen Spindichtefunktionaltheorie berechnet. Dadurch wird eine Parametrisierung und Modellierung des Effekt in den Systemen möglich, die wegen ihrer größe einen direkten ab-initio Zugang ausschließen.The magnetoelectric effect in metallic nanostructures is investigated. Thereby the change of the magnetocrystalline surface anisotropy energy of thin metallic films is calculated in the framework of the spin density functional theory as a function of external electric fields. This allows a parameterization and modelling of the effect in the systems which exclude a direct ab-initio treatment due to their size

Ferroelectric Control of Magnetocrystalline Anisotropy at Cobalt/Poly(vinylidene fluoride) Interfaces

Electric field control of magnetization is one of the promising avenues for achieving high-density energy-efficient magnetic data storage. Ferroelectric materials can be especially useful for that purpose as a source of very large switchable electric fields when interfaced with a ferromagnet. Organic ferroelectrics, such as poly(vinylidene fluoride) (PVDF), have an additional advantage of being weakly bonded to the ferromagnet, thus minimizing undesirable effects such as interface chemical modification and/or strain coupling. In this work we use first-principles density functional calculations of Co/PVDF heterostructures to demonstrate the effect of ferroelectric polarization of PVDF on the interface magnetocrystalline anisotropy that controls the magnetization orientation. We show that switching of the polarization direction alters the magnetocrystalline anisotropy energy of the adjacent Co layer by about 50%, driven by the modification of the screening charge induced by ferroelectric polarization. The effect is reduced with Co oxidation at the interface due to quenching the interface magnetization. Our results provide a new insight into the mechanism of the magnetoelectric coupling at organic ferroelectric/ferromagnet interfaces and suggest ways to achieve the desired functionality in practice