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

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 show our approach to synthesize Nd1-xSrxNiO2 (x = 0, 0.05 and 0.2) thin films with and without a SrTiO3 capping-layer. Our infinite-layer nickelate thin films were characterized by 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. Our 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.

Charge Distribution across Capped and Uncapped Infinite‐Layer Neodymium Nickelate Thin Films

“…The STO capping layer of three unit cells, when present, had been grown just after the perovskite nickelate and prior to the topotactic reduction as already mentioned elsewhere. [28] High Resolution STEM-EELS and 4D-STEM: Cross sectional transition electron microscopy (TEM) lamellae were prepared using a focused ion beam (FIB) technique (D. Troadec at IEMN facility Lille, France and at C2N, University of Paris-Saclay, France). Before FIB lamellae preparation, around 20 nm of amorphous carbon was deposited on top for protection.…”

Superconducting Nd 1− x Eu x NiO 2 thin films using in situ synthesis

“…After solid-state reduction with Al, this lattice constant decreases to 3.31 Å (Fig. 2B) due to the removal of apical oxygen from the rare earth layer, as is commonly observed in the synthesis of square-planar nickelates (5,6,25,26). After reduction, the Nd…”

Valence-Ordered Thin-Film Nickelate with Tri-component Nickel Coordination Prepared by Topochemical Reduction

“…Such a possible tetragonal symmetry is also confirmed by the observation along 45° projection as shown in Figure i,j. The apical oxygen removal indicatively reduces the o-o-p parameter, as is the case for infinite-layer nickelates, where the complete removal of apical oxygen results in an o-o-p parameter of ≈3.30 Å. ,− The observed o-o-p parameter of 3.63 Å in Sm 9 Ni 9 O 22 is thus associated with these oxygen deficiencies.…”