Synthesis of infinite-layer nickelates and influence of the capping-layer on magnetotransport

TL;DR

This study investigates how a SrTiO3 capping-layer affects the magnetotransport properties of Nd1-xSrxNiO2 thin films, revealing the capping-layer's key role in controlling magnetic anisotropy and hybridization effects relevant to nickelate superconductors.

Contribution

It provides new insights into the influence of capping-layers on the magnetic and electronic properties of infinite-layer nickelates, highlighting the interplay between hybridization and intra-atomic exchange coupling.

Findings

Capping-layer significantly alters magnetoresistance anisotropy.

Nd-Ni hybridization and Nd-4f/5d exchange coupling are crucial.

Capping-layer effects extend to non-magnetic nickelates.

Abstract

The recent discovery of a zero-resistance state in nickel-based compounds has generated a re-excitement about the long-standing problem in condensed matter of high-critical-temperature superconductivity, in light of the analogies between infinite-layer nickelates and cuprates. However, despite some formal valence and crystal symmetry analogies, the electronic properties of infinite-layer nickelates are remarkably original accounting, among other properties, of a unique Nd5d-Ni3d hybridization. This designates infinite-layer nickelates as a new class of oxide superconductors which should be considered on their own. Here we report about Nd1-xSrxNiO2 (x = 0, 0.05 and 0.2) thin films synthesized with and without a SrTiO3 capping-layer, showing very smooth and step-terraced surface morphologies. Angle-dependent anisotropic magnetoresistance measurements performed with a magnetic field rotating in-plane or out-of-plane with respect to the sample surface, rendered important information about the magnetic properties of undoped SrTiO3-capped and uncapped samples. The results point at a key role of the capping-layer in controlling the magnitude and the anisotropy of the anisotropic magnetoresistance properties. We discuss this control in terms of a combined effect between the Nd-Ni hybridization and an intra-atomic exchange coupling between the Nd-4f and Nd-5d states, the latter essentially contributing to the (magneto)transport. Further studies foresee the influence of the capping layer on infinite-layer nickelates with no magnetic rare-earth.