Phase separation, competition, and volume-fraction control in NaFe1-xCoxAs
Phase separation, competition, and volume-fraction control in NaFe1-xCoxAs
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NaFe1-xCoxAs 中的相分离、竞争和体积分数控制
DOI：
10.1103/physrevb.90.144502
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发表时间：
2014-10-07
影响因子：
3.7
通讯作者：
Yu, Weiqiang
中科院分区：
文献类型：
--
作者：
Ma, Long;Dai, J.;Yu, Weiqiang
我们报告了一项详细的核磁共振 (NMR) 研究，通过在广泛的掺杂范围内结合 Na-23 和 As-75 测量来绘制 NaFe1-xCoxAs 的相图。在欠掺杂状态（x <= 0.017）中，我们发现具有鲁棒反铁磁（AFM）阶的磁相，我们将其表示为 s-AFM 相，与弱且可能接近感应的 AFM 阶（w-AFM）相共存，其体积分数 V 相似或等于 8% 近似恒定。在 x = 0.0175 处，接近最佳掺杂时，我们观察到与 s-AFM 相相关的静态反铁磁性和与 w-AFM 相关的顺磁 (PM) 相之间的相分离。 AFM 相的体积分数在冷却时增加，但通过施加 c 轴磁场可以系统地抑制尼尔温度和体积分数。当冷却到 T-c 以下时，超导性占据 PM 区域，并且其体积分数以 AFM 相为代价而增长，这证明了基于体积排除的两种有序类型的相分离。在较高掺杂度下，静态反铁磁性甚至临界 AFM 波动都被超导性完全抑制。因此，我们建立的相图包含两种不同类型的相分离，反映了原子力显微镜和超导相在实空间和动量空间中的激烈竞争。我们认为，这种严格的互斥性和超导性对磁性的鲁棒性都是 NaFeAs 极端二维性的结果。
We report a detailed nuclear magnetic resonance (NMR) study by combined Na-23 and As-75 measurements over a broad range of doping to map the phase diagram of NaFe1-xCoxAs. In the underdoped regime (x <= 0.017), we find a magnetic phase with robust antiferromagnetic (AFM) order, which we denote the s-AFM phase, cohabiting with a phase of weak and possibly proximity-induced AFM order (w-AFM) whose volume fraction V similar or equal to 8% is approximately constant. Near optimal doping, at x = 0.0175, we observe a phase separation between static antiferromagnetism related to the s-AFM phase and a paramagnetic (PM) phase related to w-AFM. The volume fraction of AFM phase increases upon cooling, but both the Neel temperature and the volume fraction can be suppressed systematically by applying a c-axis magnetic field. On cooling below T-c, superconductivity occupies the PM region and its volume fraction grows at the expense of the AFM phase, demonstrating a phase separation of the two types of order based on volume exclusion. At higher dopings, static antiferromagnetism and even critical AFM fluctuations are completely suppressed by superconductivity. Thus the phase diagram we establish contains two distinct types of phase separation and reflects a strong competition between AFM and superconducting phases both in real space and in momentum space. We suggest that both this strict mutual exclusion and the robustness of superconductivity against magnetism are consequences of the extreme two-dimensionality of NaFeAs.