Composite Domain Walls in Multiferroic Orthoferrites RFeO3

In order to analyze novel magneto-electric effects such as electric-field controlled magnetization-flips in multiferroic orthoferrites $R$FeO$_3$, we study an effective model which includes $d$-spins on Fe sites and $f$-spins on $R$ sites. Order parameters for $d$ and $f$ spins are coupled through Peierls distoritons. Ginzburg-Landau theory is applied to investigate domain wall structures of the model. As a result, we find various types of solitons corresponding to ferromagnetic, ferroelectric and composite ferromagnetic-ferroelectric domail walls. Dynamics of the domail walls under external fields will also be presented.