Infinite-layer nickelates $R_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ ($R$ = La, Pr, Nd) are a class of superconductors with structural similarities to cuprates. Although long-range antiferromagnetic order has not been observed for these materials, magnetic effects such as antiferromagnetic spin fluctuations and spin-glass behavior have been reported. Different experiments have drawn different conclusions about whether the pairing symmetry is $s$ or $d$ wave. In this paper, we applied a scanning superconducting quantum interference device (SQUID) to probe the magnetic behavior of film samples of three infinite-layer nickelates (${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{NiO}}_2$, ${\mathrm{Pr}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_2$, and ${\mathrm{Nd}}_{0.775}{\mathrm{Sr}}_{0.225}{\mathrm{NiO}}_2$) grown on ${\mathrm{SrTiO}}_3$ (STO), each with a nominal thickness of 20 unit cells. In all three films, we observed a ferromagnetic background. We also measured the magnetic susceptibility above the superconducting critical temperature in ${\mathrm{Pr}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_2$ and ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{NiO}}_2$ and identified a non-Curie-Weiss dynamic susceptibility. Both magnetic features are likely due to ${\mathrm{NiO}}_x$ nanoparticles. Additionally, we investigated superconductivity in ${\mathrm{Pr}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_2$ and ${\mathrm{Nd}}_{0.775}{\mathrm{Sr}}_{0.225}{\mathrm{NiO}}_2$, which exhibited inhomogeneous diamagnetic screening. The superfluid density inferred from the diamagnetic susceptibility in relatively homogeneous regions shows $T$-linear behavior in both samples. Finally, we observed superconducting vortices in ${\mathrm{Nd}}_{0.775}{\mathrm{Sr}}_{0.225}{\mathrm{NiO}}_2$. We determined a Pearl length of $330\mu \mathrm{m}$ for ${\mathrm{Nd}}_{0.775}{\mathrm{Sr}}_{0.225}{\mathrm{NiO}}_2$ at 300 mK, both from the strength of the diamagnetism and from the size and shape of the vortices. These results highlight the importance of considering ${\mathrm{NiO}}_x$ particles when interpreting experimental results for these films.

中文翻译：

---

无限层镍酸盐中铁磁性和超导性的扫描 SQUID 研究

无限层镍酸盐${右}_{1-X}{锶}_X{\mathrm{氧化镍}}_2$（$右$= La、Pr、Nd）是一类与铜氧化物结构相似的超导体。尽管尚未观察到这些材料的长程反铁磁有序，但已报道了反铁磁自旋涨落和自旋玻璃行为等磁效应。关于配对对称性是否成立，不同的实验得出了不同的结论$s$或者$d$海浪。在本文中，我们应用扫描超导量子干涉装置（SQUID）来探测三种无限层镍酸盐薄膜样品的磁性行为（${拉}_{0.85}{锶}_{0.15}{\mathrm{氧化镍}}_2$,${\mathrm{普罗}}_{0.8}{锶}_{0.2}{\mathrm{氧化镍}}_2$， 和${钕}_{0.775}{锶}_{0.225}{\mathrm{氧化镍}}_2$）生长于${\mathrm{钛酸锶}}_3$(STO)，每个标称厚度为 20 个单元电池。在所有三部电影中，我们都观察到了铁磁背景。我们还测量了超导临界温度以上的磁化率${\mathrm{普罗}}_{0.8}{锶}_{0.2}{\mathrm{氧化镍}}_2$和${拉}_{0.85}{锶}_{0.15}{\mathrm{氧化镍}}_2$并确定了非居里韦斯动态磁化率。这两种磁性特征可能是由于${\mathrm{氧化镍}}_X$纳米颗粒。此外，我们还研究了超导性${\mathrm{普罗}}_{0.8}{锶}_{0.2}{\mathrm{氧化镍}}_2$和${钕}_{0.775}{锶}_{0.225}{\mathrm{氧化镍}}_2$，表现出不均匀的抗磁屏蔽。从相对均匀区域的抗磁化率推断出的超流体密度表明$\mathrm{时间}$-两个样本中的线性行为。最后，我们观察到了超导涡旋${钕}_{0.775}{锶}_{0.225}{\mathrm{氧化镍}}_2$。我们确定珍珠长度为$330\mu \mathrm{米}$为了${钕}_{0.775}{锶}_{0.225}{\mathrm{氧化镍}}_2$在 300 mK 处，既来自抗磁性的强度，也来自涡流的大小和形状。这些结果凸显了考虑的重要性${\mathrm{氧化镍}}_X$在解释这些薄膜的实验结果时。