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

Abstract

We have investigated the $L{n}^{3+}$-substitution ($Ln$ = lanthanoid) effect of a quasi two-dimensional ferromagnet Sr${}_3$Fe${}_{2-x}$Co${}_x$O${}_{7-\delta }$ ($x$$=$0.5). %$L{n}^{3+}$-substitution creates antiferromagnetic insulating clusters around $L{n}^{3+}$. With increasing $L{n}^{3+}$-concentration, the ferromagnetism is gradually suppressed and the resistivity is increasing, which are ascribed to an increase in antiferromagnetic (AFM) clusters created by $L{n}^{3+}$-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 $L{n}^{3+}$-doped samples also contributes to the enhancement of the MR.

arXiv comment4 pages