物理化学学报 >> 2008, Vol. 24 >> Issue (12): 2153-2158.doi: 10.1016/S1872-1508(08)60081-9

研究论文 上一篇    下一篇

α-甘氨酸晶体的动态磁手性和磁电效应

沈新春, 王文清, 龚, 张炎   

  1. 北京大学化学与分子工程学院应用化学系, 北京分子科学国家实验室, 北京 100871; 清华大学医学院, 北京 100084; 北京大学物理学院, 北京 100871
  • 收稿日期:2008-07-07 修回日期:2008-09-30 发布日期:2008-12-04
  • 通讯作者: 王文清 E-mail:wangwqchem@pku.edu.cn

Dynamical Spin Chirality and Magnetoelectric Effect of α-Glycine

SHEN Xin-Chun, WANG Wen-Qing, GONG Yan, ZHANG Yan   

  1. Beijing National Laboratory for Molecular Sciences, Department of Applied Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China; School of Medicine, Tsinghua University, Beijing 100084, P. R. China; School of Physics, Peking University, Beijing 100871, P. R. China
  • Received:2008-07-07 Revised:2008-09-30 Published:2008-12-04
  • Contact: WANG Wen-Qing E-mail:wangwqchem@pku.edu.cn

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摘要： 利用变温直流磁化率测定, 在外加磁场强度为依1 T, 磁场平行于晶体b轴, 发现在301-302 K α-甘氨酸有动态磁手性相变. α-甘氨酸晶体的每个晶胞包含四个分子, 属于具有中心对称结构的P21/n群, 电荷中心对称, 不导电. 在晶体中, 两层之间的N+(3)—H(8)…O(1)和N+(3)—H(8)…O(2)氢键, 沿b轴相互交叉反向配对排列. 在303 K, 用原子力显微镜可观察到α-甘氨酸晶体表面分子层与层间有规则的交叉螺旋排列. 结合中子衍射确定相变机制为, 在相变温度及外加磁场H=±1 T时, α-甘氨酸中的N+(3)—H(8),电子自旋反转为(↑). 因为N+(3)—H(8)…O(1)和N+(3)—H(8)…O(2)两反向氢键的强度和键角不同, 由动态磁手性和磁电效应, 产生电荷中心不对称, 导致304 K附近的热电相变.

关键词: α-甘氨酸, 动态磁手性, 磁电效应, 热电性, 直流磁化率, 原子力显微镜

Abstract: Dynamical spin chirality of α-glycine crystal at 301-302 K was investigated by DC (direct current)-magnetic susceptibility measurement at temperatures ranging from2 to 315 Kunder the external magnetic fields (H=±1 T) parallel to the b axis. The α-glycine crystallizes in space group P21/n with four molecules in a cell, which has centrosymmetric charge distribution. The bifurcated hydrogen bonds N+(3)—H(8)…O(1) and N+(3)—H(8)…O(2) are stacked along the b axis with different bond intensities and angles, which formanti-parallel double layers. Atomic force spectroscopy result at 303 K indicated that the surface molecular structures of α-glycine formed a regular flexuous framework in the b axis direction. The strong temperature dependence is related to the reorientation of NH+3 group and the electron spin flip-flop of (N+H) mode. Under the opposite external magnetic field of 1 T and -1 T, the electron spins of N+(3)—H(8)…O(1) and N+(3)—H(8)…O(2) flip-flop at 301-302 K. These results suggested a mechanism of the magnetoelectric effect based on the dynamical spin chirality of (N +H), which induced the electric polarization to produce the onset of pyroelectricity of α-glycine around 304 K.

Key words: α-Glycine, Dynamical spin chirality, Magnetoelectric effect, Pyroelectricity, DC-magnetic susceptibility, Atomic force spectroscopy