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arXiv 0909.1172cond-mat.str-el
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$A$位取代对Sr $_3$ Fe $_{2-x}$ Co $_x$ O $_{7-δ}$物理性能的影响

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

J. Tozawa, M. Akaki, D. Akahoshi, H. Kuwahara, K. Itatani

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摘要：

本文研究了准二维铁磁体Sr $_3$ Fe $_{2-x}$ Co $_x$ O $_{7-δ}$（$x$ $ = $ 0.5）的$Ln^{3+}$取代（$Ln$ =镧系元素）效应. % $Ln^{3+}$ -取代在$Ln^{3+}$周围产生反铁磁绝缘簇。随着$Ln^{3+}$ -浓度的增加，铁磁性逐渐被抑制，电阻率增加，这归因于由$Ln^{3+}$ -取代产生的反铁磁（AFM）团簇的增加。在Sr $_{2.7}$ Gd $_{0.3}$ Fe $_{1.5}$ Co $_{0.5}$ O $_{7-δ}$中，与Sr $_3$ Fe $_{1.5}$ Co $_{0.5}$ O $_{7-δ}$相比，磁电阻（MR）增强了约20%。铁磁（FM）相和AFM相的共存对磁电阻的增强是必不可少的。施加的磁场使FM簇在相同方向上对齐，从而导致电阻率降低。在$Ln^{3+}$掺杂样品中观察到的变磁转变也有助于MR的增强。

英文摘要：

We have investigated the $Ln^{3+}$-substitution ($Ln$ = lanthanoid) effect of a quasi two-dimensional ferromagnet Sr$_3$Fe$_{2-x}$Co$_x$O$_{7-δ}$ ($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$_{7-δ}$, the magnetoresistance (MR) is enhanced by about 20 % compared with that of Sr$_3$Fe$_{1.5}$Co$_{0.5}$O$_{7-δ}$. 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.

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