We clarify that the antiferromagnetic order in the distorted tetrahedral quasi-onedimensional spin system induces electric polarization. In this system, the effects of low dimensionality and magnetic frustration are expected to appear simultaneously. We obtain the magnetic-field-temperature phase diagram of Cu 3 Mo 2 O 9 by studying the dielectric constant and spontaneous electric polarization. Around the tricritical point at 10 T and 8 K, the change in the direction of electric polarization causes a colossal magnetocapacitance. We calculate the charge redistribution in a small spin cluster consisting of two magnetic tetrahedra to demonstrate the electric polarization induced by the antiferromagnetism. KEYWORDS: multiferroic materials, frustrating magnet, charge redistribution, Mott insulator, distorted tetrahedral spin systemSince the discovery of a strong magnetoelectric effect in TbMnO 3 , 1) multiferroics in transition-metal oxides have been extensively studied.2) In the cases of the inverse Dzyaloshinskii-Moriya interaction in a spiral spin structure [3][4][5] and the inverse Kanamori-Goodenough interaction in a collinear one, 6) the formation of the magnetic *

No abstract

We study the multiferroic properties in the distorted tetrahedral quasi-one dimensional spin system Cu3Mo2O9, in which the effects of the low dimensionality and the magnetic frustration are expected to appear simultaneously.We clarify that the antiferromagnetic order is formed together with ferroelectric properties at TN = 7.9 K under zero magnetic field and obtain the magnetic-field-temperature phase diagram by measuring dielectric constant and spontaneous electric polarization. It is found that the antiferromagnetic phase possesses a spontaneous electric polarization parallel to the c axis when the magnetic field H is applied parallel to the a axis. On the other hand, there are three different ferroelectric phases in the antiferromagnetic phase for H parallel to the c axis.

No abstract