Dynamical Spin Chirality and Magnetoelectric Effect of α-Glycine

·Xinchun Shen^a,

·Wenqing Wang^a,,,

·Yan Gong^b,

·Yan Zhang^c

doi:10.1016/S1872-1508(08)60081-9

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Abstract

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 intensities 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 NH³⁺ 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.