Single E-type collinear spin state in orthorhombic YMnO3

We studied the ferroelectricity and magnetic ordering of multiferroic orthorhombic perovskite YMnO3 using magnetic and dielectric measurements and polarized/unpolarized neutron diffraction experiments with a single crystal. The ferroelectric polarization of a relatively large value P <^> 0.55 ??C/cm2 was observed below T = 29 K. The magnetic k vector was identified ask = (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 YMnO3.