Competing Exchange Interactions in the Multiferroic and Ferrimagnetic   CaBaCo$_4$O$_7$
  Competing exchange interactions can produce complex magnetic states together with spin-induced electric polarizations. With competing interactions on alternating triangular and kagome layers, the swedenborgite CBO may have one of the largest measured spin-induced polarizations of about 1700 nC/cm$^2$ below its ferrimagnetic transition temperature at 70 K. Powder neutron-diffraction data, magnetization measurements, and spin-wave resonance frequencies in the THz range reveal that the complex spin order of multiferroic CBO can be described as a triangular array of c-axis chains ferrimagnetically coupled to each other in the ab plane. Magnetostriction on bonds that couple those chains produces the large spin-induced polarization of CBO. 
R.S. Fishman, S. Bord\'acs, V. Kocsis, I. K\'ezsm\'arki, J. Viirok, U.   Nagel, T. R\~o\~om, A. Puri, U. Zeitler, Y. Tokunag...
cond-mat.mtrl-sci