${\mathrm{BaFe}}_2{\mathrm{S}}_3$ is a quasi-one-dimensional antiferromagnetic insulator that becomes superconducting under hydrostatic pressure. The magnetic ordering temperature $T_N$, as well as the presence of superconductivity have been found to be sample dependent. It has been argued that the Fe content may play a decisive role, with the use of 5 mol% ($\delta =0.1$) excess Fe being reportedly required during the synthesis to optimize the magnetic ordering temperature and the superconducting properties. However, it is yet unclear whether a Fe off-stoichiometry is actually present in the samples, and how it affects the structural, magnetic, and transport properties. Here, we present a systematic study of compositional, structural, and physical properties of ${\mathrm{BaFe}}_{2+\delta }{\mathrm{S}}_3$ as a function of the nominal Fe excess $\delta$. As $\delta$ increases, we observe the presence of an increasing fraction of secondary phases but no systematic change in the average composition or crystal structure of the main phase. Magnetic susceptibility curves are influenced by the presence of magnetic secondary phases. While a small excess Fe (2.5 mol%, i.e., $\delta =0.05$) can slightly increase $T_N$ and decrease the temperature of the resistivity anomaly at $T^{*}$, a range of $T_N^{\prime }\mathrm{s}/T^{*}$'s is observed within each batch. This result strongly contrasts with the previously reported maximum of $T_N$ at $\delta =0.1$. Rather than with the value of $\delta$, $T_N$ and $T^{*}$ seem to correlate with the broadening in the logarithmic derivative of the resistivity around $T_N$ that could be an indicator of the level of disorder in the samples. Finally, we show that crystals free of ferromagnetic secondary phases can be obtained by remelting samples with nominal $\delta =0.05$ in a Bridgman-like process based on optical heating.

中文翻译：

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重新审视 Fe 过量对 BaFe2S3 合成的影响

${\mathrm{BaFe}}_2{\mathrm{秒}}_3$是一种准一维反铁磁绝缘体，在静水压力下变得超导。磁性有序温度${吨}_N$，以及超导性的存在已被发现与样品有关。有人认为 Fe 含量可能起决定性作用，使用 5 mol% ($\delta =0.1$) 据报道，在合成过程中需要过量的 Fe 来优化磁有序温度和超导特性。然而，目前尚不清楚样品中是否确实存在 Fe 偏离化学计量，以及它如何影响结构、磁性和传输特性。在这里，我们对材料的组成、结构和物理性质进行了系统的研究。${\mathrm{BaFe}}_{2+\delta }{\mathrm{秒}}_3$ 作为标称 Fe 过量的函数 $\delta$. 作为$\delta$增加，我们观察到第二相的比例增加，但主相的平均组成或晶体结构没有系统变化。磁化率曲线受磁性二次相的影响。而少量过量的 Fe（2.5 mol%，即$\delta =0.05$) 可以稍微增加 ${吨}_N$ 并降低电阻率异常的温度 ${吨}^{*}$, 范围 ${吨}_N^{\prime }\mathrm{秒}/{吨}^{*}$在每批中观察到 's。这一结果与之前报道的最大值形成鲜明对比${吨}_N$ 在 $\delta =0.1$. 而不是价值$\delta$, ${吨}_N$ 和 ${吨}^{*}$ 似乎与周围电阻率的对数导数的扩大有关 ${吨}_N$这可能是样本中无序程度的指标。最后，我们表明可以通过用标称重熔样品获得不含铁磁次级相的晶体。$\delta =0.05$ 在基于光学加热的类似布里奇曼的过程中。