Neutron Diffraction Study of Successive Magnetic Phase Transitions in Ferroelectric TbMn_2O_5(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Neutron diffraction measurements have been performed on a single crystal of TbMn_2O_5 to elucidate the interplay between magnetic ordering and ferroelectncity. On cooling below T_<N1>=42 K, the system enters a lock-in commensurate magnetic (CM) state with the magnetic propagation vector q=(1/2, 0, 1/4) from a two-dimensionally modulated (2D) incommensurate magnetic (ICM) one with the temperature-dependent q=(q_x O, q_z). Unlike isomorphous YMn_2O_5 and ErMn_2O_5 where a 1D-ICM phase with q=(q_x, 0, 1/4) appears and separates both 2D-ICM and CM phases, the CM phase coexists with the 2D-ICM one at temperatures between T=36.5 and 378 K, associated with a kink and a sharp peak in the dielectric constant along the b axis. On further cooling, the system reenters an ICM state at T=22.4 K whose q is pinned at (20/41, 0, 5/16) at low temperatures. The comparison between the temperatures of dielectric anomalies and magnetic phase transitions indicates that the formation of the CM ordering is related to the appearance of ferroelectricity in TbMn_2O_5, while that of the ID-ICM ordering is so in YMn_2O_5 and ErMn_2O_5.
一般社団法人日本物理学会の論文
2004-12-15