Realization of Giant Magnetoelectricity in Helimagnets

Abstract

We show that low field magnetoelectric (ME) properties of helimagnets ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{1.5}{\mathrm{Zn}}_{2}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{)}_{12}{\mathrm{O}}_{22}$ can be efficiently tailored by the Al-substitution level. As $x$ increases, the critical magnetic field for switching electric polarization is systematically reduced from $\ensuremath{\sim}1\text{ }\text{ }\mathrm{T}$ down to $\ensuremath{\sim}1\text{ }\text{ }\mathrm{mT}$, and the ME susceptibility is greatly enhanced to reach a giant value of $2.0\ifmmode\times\else\texttimes\fi{}{10}^{4}\text{ }\text{ }\mathrm{ps}/\mathrm{m}$ at an optimum $x=0.08$. We find that control of the nontrivial orbital moment in the octahedral Fe sites through the Al substitution is crucial for fine-tuning the magnetic anisotropy and obtaining the conspicuously improved ME characteristics.