Complete phase diagram of rare-earth nickelates from first-principles

Abstract

The structural, electronic and magnetic properties of AMO 3 perovskite oxides, where M is a 3d transition metal, are highly sensitive to the geometry of the bonds between the metal-d and oxygen-p ions (through octahedra rotations and distortions) and to their level of covalence. This is particularly true in rare-earth nickelates RNiO 3 that display a metal-insulator transition with complex spin orders tunable by the rare-earth size, and are on the border line between dominantly ionic (lighter elements) and covalent characters (heavier elements). Accordingly, computing their ground state is challenging and a complete theoretical description of their rich phase diagram is still missing. Here, using first-principles simulations, we successfully describe the electronic and magnetic experimental ground state of nickelates. We show that the insulating phase is characterized by a split of the electronic states of the two Ni sites (i.e., resembling low-spin 4+ and high-spin 2+) with a concomitant shift of the oxygen-2p orbitals toward the depleted Ni cations. Therefore, from the point of view of the charge, the two Ni sites appear nearly identical whereas they are in fact distinct. Performing such calculations for several nickelates, we built a theoretical phase diagram that reproduces all their key features, namely a systematic dependence of the metal-insulator transition with the rare-earth size and the crossover between a second to first order transition for R = Pr and Nd. Finally, our results hint at strategies to control the electronic and magnetic phases of perovskite oxides by fine tuning of the level of covalence.npj Quantum Materials (2017) 2:21 ; doi:10.1038/s41535-017-0024-9 INTRODUCTIONTransition metal oxides with an AMO 3 perovskite structure have attracted widespread interest over the last decades, both from academic and application points of view. This can be ascribed to their wide range of functionalities that originates from the interplay between lattice, electronic, and magnetic degrees of freedom.1 Among all perovskites, rare-earth nickelates R 3+ Ni 3+ O 3 (R = Lu-La, Y) might be considered as a prototypical case because they posses almost all possible degrees of freedom present in these materials. Nickelates were intensively studied during the nineties 2, 3 and have regained interest in the last few years due to their great potential for engineering novel electronic and magnetic states.

Overlooked Transportation Anisotropies in d-Band Correlated Rare-Earth Perovskite Nickelates

“…This observation contradicts the conventional expectations for ReNiO 3 that the elevation in T MIT should reduce the transition sharpness and variation in the resistivity across MIT [10][11][12][13][14][20][21][22] . More interestingly, the T MIT observed for the bi-axial compressively strained SNO/LAO (110) is higher than the strain relaxed SNO/STO(110), and this also differs from the previous observations that the strained SNO/LAO(001) should exhibit a lower T MIT than the strain relaxed SNO/STO(001) [10,11,20,23,25] . The above results indicate the orientation-dependent orbital re-configurations via imparting asymmetric bi-axial distortions, which is more complicated than the previous understanding for SNO only grown on the STO or LAO at (001) orientations.…”

“…In contrast to conventional semiconductors, the electronic transportation within the insulating phase of ReNiO 3 is associated to the carrier hopping among the NiO 6 octahedron [11,20] . As compared to conventional semiconductors exhibiting a relatively constant band gap (see their R-T tendency as shown Figure S6, supporting information), the energy barrier impeding the carrier hopping among the NiO 6 octahedrons within the insulating phase of ReNiO 3 is temperature dependent [10] .…”

“…As a result, the thermodynamically metastable SNO can heterogeneous nuclei and co-lattice grow on the lattice template of LaAlO 3 planes [10] . Figure 1a [9][10][11][12]20] . Therefore, an anisotropic transportation behavior is expected by confining carrier transports within the in-plane directions.…”

Oxygen-vacancy tuning of magnetism in SrTi0.75Fe0.125Co0.125O3−δOpazo1, Ong2, Vargas3 et al. 2019Phys. Rev. Materials43270View full textAdd to dashboardCite

“…compares the radially-integrated charge at the oxygen sites with the charge at the "center" of the vacancy. The reorganization of the available charge mimics the charge balance and self-regulation of transition metals in halide perovskites, rare-earth nickelates, embedded or semiconducting crystals and titanium-based oxides [44][45][46][47], nevertheless, as we discuss below, the electronic-charge changes responsible for the resulting mixed valence spin states do not impede the self-regulation-like mechanism of the transition-metal total charge.…”

Complex Magnetic Order in Nickelate Slabs

“…15 It is thus of great importance to devise new experimental tests of theoretical concepts describing the unusual magnetism of the nickelates and its interplay with the bond-order instability. 21,22 In the present work we introduce NdNiO 3 slabs oriented along the magnetic propagation vector q 0 as a specifically designed magnetic model system where the spin configuration and the magnetic moment amplitudes can be manipulated and tested against theory. The slabs were realized in thin film structures with exceptionally high quality, exhibiting virtually no defects over lateral length scales of ∼ 100 nm (see the Methods section).…”