Single E -type collinear spin state in orthorhombic YMnO3

We studied the ferroelectricity and magnetic ordering of multiferroic orthorhombic perovskite ${\mathrm{YMnO}}_{3}$ using magnetic and dielectric measurements and polarized/unpolarized neutron diffraction experiments with a single crystal. The ferroelectric polarization of a relatively large value $P\ensuremath{\simeq}0.55\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{cm}}^{2}$ was observed below $T=29\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The magnetic $\mathbit{k}$ vector was identified as $\mathbit{k}=(0,0.487,0)$ in the low-temperature ferroelectric phase. Based on the spherical neutron polarimetry experiment, the magnetic structure was determined to be of collinear $E$-type ordering with spins along the $b$ axis. The $E$-type state did not coexist with other states in the low-temperature ferroelectric phase. A simple domain structure model indicated that a single collinear $E$-type structure with a small incommensurability can be realized as the magnetic ground state of ${\mathrm{YMnO}}_{3}$.