  Magnetoelectric and magnetoelastic phenomena correlated with a phase
transition into noncollinear magnetic phase have been investigated for single
crystals of CuFeO2 with a frustrated triangular lattice. CuFeO2 exhibits
several long-wavelength magnetic structures related to the spin frustration,
and it is found that finite electric polarization, namely inversion symmetry
breaking, occurs with noncollinear but not at collinear magnetic phases. This
result demonstrates that the noncollinear spin structure is a key role to
induce electric polarization, and suggests that frustrated magnets which often
favor noncollinear configurations can be plausible candidates for
magnetoelectrics with strong magnetoelectric interaction.
