Scanning SQUID study of ferromagnetism and superconductivity in infinite-layer nickelates

Ruby A. Shi; Bai Yang Wang; Yusuke Iguchi; Motoki Osada; Kyuho Lee; Berit H. Goodge; Lena F. Kourkoutis; Harold Y. Hwang; Kathryn A. Moler

doi:10.1103/PhysRevMaterials.8.024802

Scanning SQUID study of ferromagnetism and superconductivity in infinite-layer nickelates

Ruby A. Shi, Bai Yang Wang, Yusuke Iguchi, Motoki Osada, Kyuho Lee, Berit H. Goodge, Lena F. Kourkoutis, Harold Y. Hwang, Kathryn A. Moler

DOI 10.1103/PhysRevMaterials.8.024802 · Physical Review Materials

T1

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Abstract

Infinite-layer nickelates R1−xSrxNiO2 (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 (La0.85Sr0.15NiO2, Pr0.8Sr0.2NiO2, and Nd0.775Sr0.225NiO2) grown on SrTiO3 (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 Pr0.8Sr0.2NiO2 and La0.85Sr0.15NiO2 and identified a non-Curie-Weiss dynamic susceptibility. Both magnetic features are likely due to NiOx nanoparticles. Additionally, we investigated superconductivity in Pr0.8Sr0.2NiO2 and Nd0.775Sr0.225NiO2, 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 Nd0.775Sr0.225NiO2. We determined a Pearl length of 330µm for Nd0.775Sr0.225NiO2 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 NiOx particles when interpreting experimental results for these films.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Nd0.775Sr0.225NiO2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5.1	Pressure not reported	zero_resistance
Pr0.8Sr0.2NiO2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.8	Pressure not reported	zero_resistance
La0.85Sr0.15NiO2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8	Pressure not reported	onset
La0.85Sr0.15NiO2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	2	Pressure not reported	zero_resistance
Nd0.8Sr0.2NiO2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
La0.8Ca0.2NiO2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
La0.8Sr0.2NiO2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown