Quantitative calculations of polarizations arising from the symmetric and antisymmetric exchange strictions in Tm-doped GdMnO_3

The ferroelectric polarization and phase diagram in Tm-doped Gd MnO3 are studied by means of Monte Carlo simulation based on the Mochizuki–Furukawa model. Our work well reproduces the low temperature polarization at various substitution levels observed experimentally. It is demonstrated that the Tm-doping can control the multiferroic behaviors through modulating the spin structures, resulting in the flop of the electric polarization. In addition, the polarization in the ab-plane cycloidal spin phase arises from comparable contributions of the symmetric exchange striction and antisymmetric exchange striction, leading to much bigger polarization than that in the bc-plane cycloidal spin phase where only the contribution of the latter striction is available. The phase diagram obtained in our simulation is helpful for clarifying the multiferroic properties in doped manganite systems and other related multiferroics.