Microscopic origin of the simultaneous ferroelectric and magnetic phase transition of RMn_2O_5

(1)RMn2O5(R=Er，Tb，Ho，Tm)的磁传播矢量Q_M。(2)建立了同时测量QM、介电常数E和电极化Ps的方法。(3)RMn2O5介电常数的再研究。发现了广义相图。(4)同步辐射X射线实验找到了与铁电相对应的新的布拉格反射。(5)HoMn_2O_5的偏振中子散射测量了自旋手性。(6)在外加磁场的低温下，HoMn_2O_5和ErMn_2O_5的中子散射实验证实了RMN_2O_5中连续的磁性和铁电相变发生在相同的温度。此外，我们还证明了RMn2O5的第一铁电相变具有相同的性质，而与RMn2O5中的稀土元素R无关。另一方面，在最低温区的巨型电磁效应强烈地依赖于RMn2O5。我们有S…更重要的是，在外加磁场的作用下，磁有序产生了这样的巨磁效应。也就是说，磁有序引起铁电极化。这项研究成果由《日本物理学会杂志》颁发。在同时测量了Q_M、ε和Ps之后，我们感觉我们提出的假设必须稍微改变一下，因为在一维慢化磁相和磁公度相之间看到了非常弱的铁电成分。测量部分的电极化显示在磁公度相以下。这种现象可能与所谓不公度的存在有关。我们还进行了同步加速器x射线衍射，以了解铁电相的真实结构。晶胞尺寸沿c方向加倍，空间群为Pb2_1m。在(001/2)和(000)位置测量到非常弱的新布拉格反射，其强度比基本布拉格反射弱8个数量级。较少

We performed the following investigations and published the results.(1)Magnetic propagation vectors q_M of RMn_2O_5(R=Er, Tb, Ho, Tm).(2)Developing the method to measure q_M, dielectric constant E and electric polarization Ps simultaneously.(3)Reinvestigation of the dielectric constant of RMn_2O_5,and found the generalized phase diagram.(4)Synchrotron x-ray experiments to find new Bragg reflections corresponding to the ferroelectric.(5)Polarized neutron scattering of HoMn_2O_5 to measure the spin-chirality.(6)Neutron scattering experiments of HoMn_2O_5 and ErMn_2O_5 at low temperature under external magnetic field.We confirmed that the successive magnetic and ferroelectric phase transitions in RMn_2O_5 occur at the same temperatures. Further, we show that the first ferroelectric phase transition has the same character regardless of the rare earth element R of RMn_2O_5. On the other hand, the giant electro-magnetic effect at the lowest temperature region strongly depends on R. We have s … More hown that the magnetic ordering under the external magnetic field induces such giant electro-magnetic effect. That is, magnetic ordering induces ferroelectric polarization. This result was awarded by Journal of the Physical Society of Japan. After the simultaneous measurements of q_M,ε and Ps, we have the feeling that the scenario we proposed must be changed slightly since very weak ferroelectric component is seen between the one-dimensionally moderated magnetic phase and magnetic commensurate phase. Measure part of the electric polarization shows up below the magnetic commensurate phase. Such phenomena might be related to the existence of the so-called discommensuration. We also performed synchrotron x-ray diffraction to know the true structure at the ferroelectric phase. The unit cell size is double along c-direction and the space group is Pb2_1m. Very weak new Brag reflections were measured at (001/2) and (000) positions, whose intensities are 8-order magnitude weaker than the fundamental Bragg reflections. Less