Tuning the spontaneous exchange bias effect with Ba to Sr partial substitution in La$_{1.5}$(Sr$_{0.5-x}$Ba$_{x}$)CoMnO$_{6}$

TL;DR

This study explores how partial Ba to Sr substitution in La$_{1.5}$(Sr$_{0.5-x}$Ba$_{x}$)CoMnO$_{6}$ double-perovskites enhances the spontaneous exchange bias effect by modifying magnetic phases and increasing magnetic moments.

Contribution

It demonstrates that Ba to Sr substitution in La-based double-perovskites significantly enhances the exchange bias effect through structural and magnetic phase modifications.

Findings

Exchange bias field increases with intermediate Sr/Ba concentrations.

Ba to Sr substitution raises the effective magnetic moment and AFM transition temperature.

Enhanced Co$^{3+}$ high-spin fraction correlates with increased AFM phase and exchange bias.

Abstract

The spontaneous exchange bias (SEB) effect is a remarkable phenomenon recently observed in some reentrant spin-glass materials. Here we investigate the SEB in La$_{1.5}$(Sr$_{0.5-x}$Ba$_{x}$)CoMnO$_{6}$ double-perovskites, a system with multifarious magnetic phases for which a notable increase in the exchange bias field is observed for intermediate Sr/Ba concentrations. The Ba to Sr substitution leads to the enhancement of the crystal lattice, which is accompanied by the raise of both the effective magnetic moment ($\mu_{eff}$) and the antiferromagnetic (AFM) transition temperature that is observed below the ferromagnetic ordering. Such increases are likely related to the increased fraction of Co$^{3+}$ in the high spin configuration, leading to the enhancement of Co$^{3+}$--O--Mn$^{4+}$ AFM phase and to the reduction in the uncompensation of the AFM coupling between Co and Mn. The combined effect of the increased $\mu_{eff}$ and AFM phase plausible explains the changes in the SEB effect.