Type-II multiferroic is an important area in the big family of multiferroics, in which its polarization originates from the spin order, resulting in a strong magnetoelectric coupling. Here we briefly review the previous mechanisms of the spin-order induced polarization, including the Katsura–Nagaosa–Balatsky (KNB) model, inverse Dzyaloshinskii-Moria (DM) interaction model, exchange striction model, and the bond polarization model. 

Then our unified polarization model is discussed in detail, which contains pure electronic, ion displacement and lattice deformation contributions. And a feasible approach for constructing the unified model based on the first-principles calculations is presented. With this model, we unravel the microscopic mechanisms of the ferroelectricity in several typical multiferroics. New type-II multiferroics with strong magnetoelectric coupling and giant polarization are expected to be discovered and/or designed through the use of this model.

This paper was originally published in Computational Materials 112, Part B, (2016) 448-458