摘要
利用变温直流磁化率测定,在外加磁场强度为±1T,磁场平行于晶体b轴,发现在301-302Kα-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303K,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=±1T时,α-甘氨酸中的N+(3)—H(8),电子自旋反转为(邙).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304K附近的热电相变.
Dynamical spin chirality of α-glycine crystal at 301-302 K was investigated by DC （direct current）- magnetic susceptibility measurement at temperatures ranging from 2 to 315 K under 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 intensifies and angles, which form anti-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^＋ 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.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2008年第12期2153-2158,共6页
Acta Physico-Chimica Sinica
基金
国家基础研究重大项目(2004-973-36)
国家自然科学基金(20452002)资助
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
α-Glycine
Dynamical spin chirality
Magnetoelectric effect
Pyroelectricity
DC-magnetic susceptibility
Atomic force spectroscopy
