Giant linear magnetoelectric effect at the morphotropic phase boundary of epitaxial ${\mathrm{Sr}}_{0.5}{\mathrm{Ba}}_{0.5}{\mathrm{MnO}}_3$ films

First-principles calculations are conducted to compute linear magnetoelectric coupling coefficients in epitaxial (001) ${\mathrm{Sr}}_{0.5}{\mathrm{Ba}}_{0.5}{\mathrm{MnO}}_3$ films. A large enhancement of different linear magnetoelectric elements is found in a strained-induced morphotropic phase boundary region. Such enhancement is demonstrated to originate from the behavior of the dielectric susceptibility, thanks to a simple phenomenological model that is presently shown to be relevant and accurate. This work can thus provide a promising approach towards designing highly desired single-phase multiferroic with a colossal magnetoelectric conversion.

Figure 1

Properties of SBMO films as a function of their in-plane lattice parameter in the $I4mm,Cm$, and $Imm2$ structural states: (a) the total energy, and (b) linear magnetoelectric coupling components. The zero of energy in (a) corresponds to the lowest energy structure, having $a_{\mathrm{ip}}=3.919\AA$. The inset in (a) shows the lowest optical frequency at the Γ point as a function of the in-plane lattice parameter. α values of four representative materials are also indicated by arrows on the vertical axis of (b) [37, 38].

Figure 2

Computed linear magnetoelectric coupling coefficients $({\alpha }_{yz}$ and ${\alpha }_{zy})$ as a function of $a_{\mathrm{ip}}$ with its corresponding fitted values $({\alpha }_{yz}={\alpha }_{yz}^{\left(1\right)}+{\alpha }_{yz}^{\left(2\right)}=-g_{zxy}{\chi }_{yy}^P{L}_x{\chi }_{zz}^M-4{\varepsilon }_0{\lambda }_{yz}{P}_y{\chi }_{yy}^P{M}_z{\chi }_{zz}^M$ and ${\alpha }_{zy}={\alpha }_{zy}^{\left(1\right)}+{\alpha }_{zy}^{\left(2\right)}=-g_{yxz}{\chi }_{zz}^P{L}_x{\chi }_{yy}^M-4{\varepsilon }_0{\lambda }_{zy}{P}_z{\chi }_{zz}^P{M}_y{\chi }_{yy}^M)$ using Eqs. (1) in the $I4mm,Cm$, and $Imm2$ phases.

Figure 3

Dielectric (a) and magnetic susceptibility (b) tensor components of epitaxial (001) SBMO films as a function of $a_{\mathrm{ip}}$ in $I4mm,Cm$, and $Imm2$ states. The inset in (b) shows the polarization values of SBMO films as a function of $a_{\mathrm{ip}}$.