平成２９年度（２０１７年度）第8回 物理教室談話会

題目	Neutron scattering experiments in a new multiferroic molecular magnet
講師	Javier Campo 氏 (University of Zaragoza, Spain))
日時	平成29年12月5日(火)　15：30～
場所	理学部２１講義室 （理学部１号館２階）
概要	The family of antiferromagnetic A2[FeCl5(H2O)] compounds (A = alkali metal or ammonium ion) has awakened a renewed interest owing to the recent observation of multiferroicity in some of its members.[1], [2] We have recently investigated by means of single crystal and powder neutron diffraction the magnetic structure of (ND4)2[FeCl5(D2O)] (with properties completely equivalent to the hydrogenated form) in order to understand the underlying mechanism of multiferroicity in this compound. This material orders antiferromagnetically at TN = 7.25 K and multiferroicity arises below ca. 6.9 K with the onset of ferroelectric order. We have observed at zero magnetic field a cycloidal magnetic structure propagating in the c-axis with k = (0, 0, 0.23) and with the magnetic moments lying in the ac plane (Fig.1). This cycloid would be at the origin of the magneto-electric coupling via inverse Dzyaloshinsky–Moriya interaction [3]. Also the evolution of the magnetic structure with increasing the magnetic field has been determined by the use of neutron diffraction under applied magnetic field. It shows three different regions including a lock-in of the propagation vector for fields between 2.5 and 5 T. Figure 1: View along the ac plane of magnetic structures of (ND4)2[FeCl5(D2O)]. For the sake of clarity only Fe atoms have been represented. References [1] Ackermann M, Brüning D, Lorenz T, Becker P and Bohatý L 2013 New J. Phys. 15 123001 [2] Ackermann M, Lorenz T, Becker P and Bohatý L 2014 ArXiv :1408.3997v1 [3] Rodríguez-Velamazán J.A., Fabelo O, Campo J, Millán A, Chapon L, Johnson R, Scientific Reports | 5:14475 | DOI: 10.1038/srep14475
世話人	小林夏野（内線：8631）