Novel Striped Multiferroic Phases in Hole-Doped Manganites

After the discovery of a so-called ``spin-orthogonal stripe'' (SOS) phase in models for quarter-doped hole manganites [1], our group carried out additional computational work at other doping fractions to search for analogous multiferroic phases. Here we report the discovery of similar SOS phases at several hole dopings $x=1/N$ $(N=3,5,6...)$ using a double exchange model with spin frustration, and applying variational and Monte Carlo techniques. The full phase diagram created by varying electron-lattice and superexchange couplings also contains an exotic $C_{x}E_{1-x}$ phase. The new SOS$_{x}$ phases are intuitively explained via a rotation from the $C_{x}E_{1-x}$ zig-zag spin configuration. This creates stripes separating domains containing orthogonal spins. Because of the Dzyaloshinskii-Moriya interaction, it is conjectured that these SOS states should be ferroelectric as well. For $N$ even the spin states are similar to $N$ odd but there is a cancellation of the net ferroelectric moment. \\[4pt] [1] Shuai Dong {\it et al.}, Phys. Rev. Lett. {\bf 103}, 107204 (2009).