Role of an interfacial FeO layer in the electric-field-driven switching of magnetocrystalline anisotropy at the Fe/MgO interface

The electric-field-induced switching of magnetocrystalline anisotropy (MCA) between in-plane and out-of-plane orientations is investigated by first-principles calculations for the prototypical Fe on MgO(001) system. Our results predict that an ideal abrupt Fe/MgO interface gives rise to a large out-of-plane MCA due to weak Fe-O hybridization at the interface, but the MCA switching by an applied electric field is found to be difficult to achieve. Instead, the existence of an interfacial FeO layer plays a key role in demonstrating the MCA switching that accompanies an electric-field-induced displacement of Fe atoms on the interfacial FeO layer.

Figure 1

(Color online) Models and notation for the atomic structures of an ideal Fe/MgO(001) interface: (a) Fe/MgO and (b) ${\text{Au}}_3/{\text{Fe}}_3/\text{MgO}$ structures. The arrow at the left indicates the direction of the external electric field. An interfacial FeO layer between the Fe layer and the MgO substrate is modeled by replacing Mg atoms (Mg2) on the interface MgO layer by Fe atoms.

Figure 2

(Color online) Zero-field DOS for Fe1 atoms (thick lines) for Fe/MgO and Fe/FeO/MgO structures along with the orbital-decomposed (thin lines) DOS. Dotted-dashed, solid, and dashed lines represent $d_0$ $\left(d_{z^2}\right)$, $d_{\pm 1}$ $\left(d_{xz,yz}\right)$, and $d_{\pm 2}$ $\left(d_{x^2-y^2,xy}\right)$ orbitals, respectively.

Figure 3

(Color online) Calculated minority-spin band structures and MCA energy contribution, $E_{\text{MCA}}\left(\mathbf{k}\right)$ along high-symmetry directions for (a) Fe/MgO and (b) Fe/FeO/MgO structures in external electric fields of $-1\text{V}/\text{Å}$ (dashed lines) and $1\text{V}/\text{Å}$ (solid lines). Bands 3, 4, and 5 stand for $d_{x^2-y^2}$, $d_{xy}$, and $d_{xz,yz}$ states, respectively.

Figure 4

(Color online) (a) Dependence of $E_{\text{MCA}}$ on the oxygen concentration $x$ in the interfacial ${\text{FeO}}_x$ layer for the Au-capped Fe/MgO interfaces for external electric fields of $1\text{V}/\text{Å}$ (open circles) and $-1\text{V}/\text{Å}$ (closed circles). (b) Calculated $E_{\text{MCA}}$ as a function of the change in the number of valence electrons $\left(\Delta N\right)$ for the different systems. Dashed and solid lines represent results for an external electric field of $1\text{eV}/\text{Å}$ and $-1\text{eV}/\text{Å}$, respectively.