Magnetic transition and spin-polarized two-dimensional electron gas controlled by polarization switching in strained ${\mathrm{CaMnO}}_3/{\mathrm{BaTiO}}_3$ slabs

$Abinitio$ calculations show the presence of a strong magnetoelectric interfacial coupling in a ${\mathrm{CaMnO}}_3$ ultrathin film grown on a strained ${\mathrm{BaTiO}}_3$ ferroelectric film. This heterostructure presents a polarization driven magnetic transition from a G-type to an A-type antiferromagnetic structure. Together with this magnetic transition we find a metallic behavior at the interface between these two insulators, where the charge character of the carriers can be tuned from electrons to holes by switching the electric polarization direction of the ferroelectric film. Besides, the electron gas is spin polarized while the hole gas is not.

Figure 1

(a) Unit cell of ${\left({\mathrm{CaMnO}}_3\right)}_4/{\left({\mathrm{BaTiO}}_3\right)}_5$ heterostructure. In this sketch, the polarization is pointing to the CMO film $(\mathrm{P}\uparrow )$. (b) ${\mathrm{CaMnO}}_3{)}_4/{\left({\mathrm{BaTiO}}_3\right)}_{8.5}/{\left({\mathrm{CaMnO}}_3\right)}_4$ trilayer. The figures were generated using the vesta software package [49].

Figure 2

Layer resolved PDOS of CMO (left) and BTO (right) layers (excluding the BTO-vacuum interface), corresponding to P=0. In blue (red) the Mn $d_{x^2-y^2}$ $\left(d_{z^2}\right)$ character is shown.

Figure 3

Upper panels: layer resolved PDOS of CMO (left) and BTO (right) layers (excluding the BTO-vacuum interface) for the case of polarization pointing to the CMO interface $(\mathrm{P}\uparrow )$. Lower panels: spin up (left) and spin down (right) bandstructure of the heterostructure. The different character of the Mn's $e_g$ orbitals coming from each CMO layer is highlighted.

Figure 4

Upper panels: layer resolved PDOS of CMO (left) and BTO (right) layers (excluding the BTO-vacuum interface) for the case of polarization pointing away from the CMO interface $(\mathrm{P}\downarrow )$. Lower panels: spin ($\mathrm{up}+\mathrm{down}$) bandstructure of the heterostructure. Projections onto the Mn-$e_g$ and interfacial O(CMO) orbitals (left) and onto interfacial O $p_x+p_y$ (BTO) (right) are highlighted. Ti bands are above 2.5 eV.

Figure 5

Spin up $+$ spin down bandstructure of the trilayer corresponding to its ground state AAF-GAF. (a) Projections onto the Mn-$d_{xy}$ orbitals for the different ${\mathrm{MnO}}_2$ layers within the CMO1-film are highlighted [see Fig. 1]. (b) Projections onto the ${\mathrm{p}}_x+{\mathrm{p}}_y$ orbitals of O atoms within both CMO2 and BTO interfacial layers. Mn-$d$ orbitals are above 0.5 eV, as shown in the red-highlighted curve. (c) Calculated CB and VB profiles for the [001] direction of the trilayer. Note that layer No. 1 in this figure corresponds to layer named L4 in Fig. 1.