Switching from pyroelectric to ferroelectric order in Ni doped CaBaCo4O7

TL;DR

This study demonstrates a transition from pyroelectric to ferroelectric order in Ni-doped CaBaCo4O7, revealing strong spin-charge coupling and a change in magnetic structure associated with electric polarization switching.

Contribution

It reports the first observation of ferroelectric ordering in Ni-doped CaBaCo4O7 and links magnetic reordering to electric polarization behavior.

Findings

Ferroelectric order appears at ~82 K with enhanced polarization.

Ni doping alters magnetic interactions, leading to a non-collinear to collinear ferrimagnetic transition.

Coupling between magnetic layers influences electric polarization switching.

Abstract

We report ferroelectric ordering in Ni substituted CaBaCo4O7. Magnetization showed ferrimagnetic transition at 60 K and an additional transition is found ~ 82 K, further, enhanced antiferromagnetic interactions and decrease in saturation magnetization are noticed with Ni substitution. The dielectric and pyroelectric measurements illustrate a strong coupling between spin and charge degrees of freedom; ferroelectric behavior is confirmed with enhanced ordering temperature (~82 K) and saturation polarization (250 muC/m2. Neutron diffraction has revealed an increase in c-lattice parameter in Ni sample and all the Co/Ni moments are reoriented in a- direction; evidently a non-collinear ferrimagnetic to collinear ferrimagnetic spin order is observed. The coupling between the triangular and Kagome layers weakens and leads to up-up-down-down AFM ordering in the Kagoma layer. This can be viewed as a 2D-collinear layer with unequal bond distances and most likely responsible for the switching of electric polarization.