Dynamical Spin Chirality and Magnetoelectric Effect of α-Glycine

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.