# Metamagnetism stabilized giant magnetoelectric coupling in ferroelectric \textit{x}BaTiO${_3}$-(1-\textit{x})BiCoO${_3}$ solid solution

## TL;DR

This study reveals how metamagnetism stabilizes giant magnetoelectric coupling in a ferroelectric solid solution of BaTiO3 and BiCoO3, with properties tunable by composition and volume, highlighting pressure-induced spin transitions and their impact on multiferroicity.

## Contribution

It demonstrates the stabilization of metamagnetic states and strong magnetoelectric coupling in the extit{x}BaTiO${_3}$-(1- extit{x})BiCoO${_3}$ system, revealing composition-dependent spin transitions and ferroelectric properties.

## Key findings

- Metamagnetic spin state transitions linked to ferroelectric transitions.
- Pressure induces high spin to low spin transition in x=0.33 composition.
- Ferroelectric polarization decreases with increasing BaTiO3 concentration.

## Abstract

In order to establish the correlation between the magnetoelectric coupling and magnetic instability, we have studied the structural, magnetic, and ferroelectric properties of \textit{x}BaTiO${_3}$-(1-\textit{x})BiCoO${_3}$ as a function of BaTiO$_3$ concentration ($x$) and volume.The $G-$type antiferromagnetic ordering is found to be energetically favorable for $x<$ 0.45 and higher concentrations stabilize with nonmagnetic states. We observe metamagnetic spin state transitions associated with paraelectric to ferrolectric transitions as a function of volume and $x$ using synchrotron diffraction and computational studies, indicating a strong magnetoelectric coupling. Specifically for $x=$ 0.33 composition, a pressure induced high spin (HS) to low spin (LS) transition occurs when the volume is compressed below 5\%. Our orbital$-$projected density of states show a HS state for Co$^{3+}$ in the ferroelectric ground state for $x<$ 0.45 and the corresponding paraelectric phase is stable in the nonmagnetic state due to the stabilization of LS state as evident from our fixed$-$spin$-$moment calculations and magnetic measurements. High values of spontaneous ferroelectric polarizations are predicted for lower $x$ values which inversely vary with $x$ because of the reduction of tetragonality ($c/a$) with increase in $x$. Moreover, we find that the HS$-$LS transition point and magnetoelectric coupling strength can be varied by $x$.