Universality of the surface magnetoelectric effect in half-metals

An electric field applied to a ferromagnetic metal produces a surface magnetoelectric effect originating from the spin-dependent screening of the electric field which results in a change in the surface magnetization of the ferromagnet. Here we predict that if the ferromagnet is a half-metal, due to the screening charge formed solely by single-spin conducting states, the surface magnetoelectric coefficient is the universal constant ${\ensuremath{\mu}}_{B}/e{c}^{2}\ensuremath{\approx}6.44\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\text{ }\text{G}\text{ }{\text{cm}}^{2}/\text{V}$. This prediction is in excellent agreement with results of our first-principles calculations of the magnetic response of a half-metallic ${\text{CrO}}_{2}$ to an applied electric field. The universal value of the surface magnetoelectric coefficient in half-metals may be used as another tool for detecting half-metallicity.