Competing Exchange Interactions in the Multiferroic and Ferrimagnetic CaBaCo$_4$O$_7$

TL;DR

This paper investigates the complex magnetic states and large spin-induced polarization in CaBaCo$_4$O$_7$ caused by competing exchange interactions, using neutron diffraction, magnetization, and THz spin-wave data.

Contribution

It reveals the detailed spin structure and the origin of large polarization in CaBaCo$_4$O$_7$, highlighting the role of competing interactions and magnetostriction.

Findings

CaBaCo$_4$O$_7$ exhibits a spin-induced polarization of about 1700 nC/cm$^2$.

The spin order is a triangular array of c-axis chains ferrimagnetically coupled.

Magnetostriction on bonds contributes to the large polarization.

Abstract

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.