Competing Exchange Interactions in the Multiferroic and Ferrimagnetic CaBaCo4O7

Abstract

Geometric frustration can produce a non-collinear magnetic state associated with a spin-induced electric polarization. With geometric frustration on alternating triangular and kagome layers, CaBaCo4O7 may have one of the largest measured spin-induced polarizations of ∼ 1700 nC/cm2 below its ferrimagnetic transition temperature. Powder diffraction data, magnetization measurements, and THz absorption frequencies reveal that the spin state of multiferroic CaBaCo4O7 can be described as a triangular array of c-axis chains with strong coupling within each chain but weak coupling in the ab plane between chains. Magnetostriction for a set of weak spin bonds in the ab plane coupling those chains produces the large spin-induced polarization of CaBaCo4O7.