MS28-P01 Phase transition of a spiral magnetic ordering in the Fe-based double-perovskiteUsing a modified traveling solvent floating zone technique, we are able to grow a high quality single crystal of the double perovskite oxide YBaCuFeO5 for the detailed study using magnetization, dielectric constant, and neutron diffraction. We demonstrate that the crystal shows two antiferromagnetic transitions at TN1 ~475 K and TN2~175 K, and displays a giant dielectric constant with a characteristic of the dielectric relaxation at TN2. It does not show the evidence of the electric polarization for the crystal. The transition at TN1 corresponds with a paramagnetic to antiferromagnetic transition with a magnetic propagation vector doubling the unit cell along three crystallographic axes. Such a paramagnetic state at high temperatures was also confirmed by the using inelastic neutron scattering. Upon cooling, at TN2, the commensurate spin ordering transforms to a spiral magnetic structure with a propagation vector of (0.5h 0.5k 0.5l+-δ), where h, k, and l are odd, and the incommensurability is temperature dependent. Around the transition boundary at TN2, both commensurate and incommensurate spin ordering coexist.
 Yen-Chung Lai, et. al., J. of Phys.: Condensed Matter, 29, 145801 (2017).Keywords: phase transition, spiral magnetic ordering, neutron scattering