$A$-site substitution effect on physical properties of Sr$_3$Fe$_{2-x}$Co$_x$O$_{7-\delta}$

TL;DR

This study explores how substituting lanthanoid ions at the A-site in Sr$_3$Fe$_{2-x}$Co$_x$O$_{7-\delta}$ affects its magnetic and electronic properties, revealing increased antiferromagnetic clusters and enhanced magnetoresistance.

Contribution

It demonstrates the impact of lanthanoid substitution on magnetic phase coexistence and magnetoresistance in a layered ferromagnetic oxide, highlighting the role of AFM clusters.

Findings

Antiferromagnetic clusters increase with Ln$^{3+}$ substitution.

Magnetoresistance is enhanced by about 20% in Gd-doped samples.

Coexistence of FM and AFM phases is key to MR enhancement.

Abstract

We have investigated the $Ln^{3+}$-substitution ($Ln$ = lanthanoid) effect of a quasi two-dimensional ferromagnet Sr$_3$Fe$_{2-x}$Co$_x$O$_{7-\delta}$ ($x$$ = $0.5). %$Ln^{3+}$-substitution creates antiferromagnetic insulating clusters around $Ln^{3+}$. With increasing $Ln^{3+}$-concentration, the ferromagnetism is gradually suppressed and the resistivity is increasing, which are ascribed to an increase in antiferromagnetic (AFM) clusters created by $Ln^{3+}$-substitution. In Sr$_{2.7}$Gd$_{0.3}$Fe$_{1.5}$Co$_{0.5}$O$_{7-\delta}$, the magnetoresistance (MR) is enhanced by about 20 % compared with that of Sr$_3$Fe$_{1.5}$Co$_{0.5}$O$_{7-\delta}$. Coexistence of ferromagnetic (FM) and AFM phases is essential for the enhancement of the MR\@. Applied magnetic fields align the FM clusters in the same direction, resulting in a reduction in the resistivity. A metamagnetic transition observed in the $Ln^{3+}$-doped samples also contributes to the enhancement of the MR.