Electric polarization induced by Neel order without magnetic   superlattice: experimental study of Cu3Mo2O9 and numerical study of a small   spin cluster
  We clarify that the antiferromagnetic order in the distorted tetrahedral quasi-one dimensional spin system induces electric polarizations. In this system, the effects of the low dimensionality and the magnetic frustration are expected to appear simultaneously. We obtain the magnetic-field-temperature phase diagram in Cu3Mo2O9 by studying the dielectric constant and the spontaneous electric polarization. Around the tricritical point at 10 T and 8 K, the change of the direction in the electric polarization causes a colossal magnetocapacitance. We calculate the charge redistribution in the small spin cluster consisting of two magnetic tetrahedra to demonstrate the electric polarization induced by the antiferromagnetism. 
Haruhiko Kuroe, Tomohiro Hosaka, Suguru Hachiuma, Tomoyuki Sekine,   Masashi Hase, Kunihiko Oka, Toshimitsu Ito, Hiroshi Eis...
cond-mat.str-el cond-mat.mtrl-sci