Magnetic structure and electronic properties of mixed-metal Ruddlesden-Popper oxide LaSrCo$_{1/2}$Fe$_{1/2}$O$_4$

TL;DR

This study combines theoretical calculations and experimental synthesis to explore how atomic arrangements influence the magnetic and electronic properties of LaSrCo$_{1/2}$Fe$_{1/2}$O$_4$, revealing complex magnetic interactions and the importance of site-specific Hubbard U values.

Contribution

It provides a detailed analysis of the magnetic interactions and electronic structure of LaSrCo$_{1/2}$Fe$_{1/2}$O$_4$, highlighting the dependence on ion distribution and the necessity of site-specific Hubbard U parameters.

Findings

Fe-Fe exchange is antiferromagnetic.

Co-Co and Fe-Co exchanges are ferromagnetic.

Experimental magnetization shows antiferromagnetic behavior.

Abstract

Atomic, electronic, and magnetic structure of LaSrCo$_{1/2}$Fe$_{1/2}$O$_4$ mixed-metal Ruddlesden-Popper oxide is investigated theoretically using self-consistent ACBN0 DFT + $U$ approach. We show that the electronic and magnetic properties strongly depend on the distribution of transition-metal and La/Sr ions in the lattice. Fe-Fe exchange is found to be antiferromagnetic, whereas Co-Co and Fe-Co exchange is ferromagnetic. We find that Co spin states depend on the distribution in both La/Sr and transition-metal ions. The most energetically favorable configuration is ferromagnetic, whereas the majority of metastable configurations are antiferromagnetic. LaSrCo$_{1/2}$Fe$_{1/2}$O$_4$ was synthesized using spray-pyrolysis method. Magnetization measurements revealed antiferromgnetic behavior, thus indicating presence of metastable configurations in the synthesized material. In addition, we show that in complex systems, such as mixed-metal Ruddlesden-Popper phases, Hubbard $U$ values have to be determined for each crystallographically non-equivalent site.