Multiferroic behavior in the double-perovskite Lu 2 MnCoO 6

We present Lu${}_{2}$MnCoO${}_{6}$, a multiferroic member of the double perovskites that we have investigated using x-ray and neutron diffraction, specific heat, magnetization, electric polarization, and dielectric constant measurements. This material possesses a net electric polarization strongly coupled to a net magnetization below 35 K, despite the antiferromagnetic ordering of the $S=3/2$ Mn${}^{4+}$ and Co${}^{2+}$ spins in an $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$ configuration along the $c$ direction. We discuss the magnetic order in terms of a condensation of domain boundaries between $\ensuremath{\uparrow}\ensuremath{\uparrow}$ and $\ensuremath{\downarrow}\ensuremath{\downarrow}$ ferromagnetic domains, with each domain boundary producing an electric polarization due to spatial inversion symmetry breaking. In an applied magnetic field the domain boundaries slide, controlling the size of the magnetization, electric polarization, and magnetoelectric coupling.