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Abstract We provide a set of computational experiments based on ab initio calculations to elucidate whether a cuprate-like antiferromagnetic insulating state can be present in the phase diagram of the low-valence layered nickelate family (R $$_{n+1}$$ n + 1 Ni $$_n$$ n O $$_{2n+2}$$ 2 n + 2 , R= rare-earth, $$n=1-\infty$$ n = 1 - ∞ ) in proximity to half-filling. It is well established that at $$d^9$$ d 9 filling the infinite-layer ( $$n=\infty$$ n = ∞ ) nickelate is metallic, in contrast to cuprates wherein an antiferromagnetic insulator is expected. We show that for the Ruddlesden-Popper (RP) reduced phases of the series (finite n ) an antiferromagnetic insulating ground state can naturally be obtained instead at $$d^9$$ d 9 filling, due to the spacer RO $$_2$$ 2 fluorite slabs present in their structure that block the c -axis dispersion. In the $$n=\infty$$ n = ∞ nickelate, the same type of solution can be derived if the off-plane R-Ni coupling is suppressed. We show how this can be achieved if a structural element that cuts off the c -axis dispersion is introduced (i.e. vacuum in a monolayer of RNiO $$_2$$ 2 , or a blocking layer in multilayers formed by (RNiO $$_2$$ 2 ) $$_1$$ 1 /(RNaO $$_2$$ 2 ) $$_1$$ 1 ). 

The discovery of superconductivity in thin films (∼10 nm) of infinite-layer hole-doped NdNiO 2 has invigorated the field of high temperature superconductivity research, reviving the debate over contrasting views that nickelates that are isostructural with cuprates are either 1) sisters of the high temperature superconductors, or 2) that differences between nickel and copper at equal band filling should be the focus of attention. Each viewpoint has its merits, and each has its limitations, suggesting that such a simple picture must be superseded by a more holistic comparison of the two classes. Several recent studies have begun this generalization, raising a number of questions without suggesting any consensus. In this paper, we organize the findings of the electronic structures of n -layered NiO 2 materials ( n = 1 to ∞ ) to outline (ir)regularities and to make comparisons with cuprates, with the hope that important directions of future research will emerge. 

Low dimensional magnetism has been powerfully boosted as a promising candidate for numerous applications. The stability of the long-range magnetic order is directly dependent on the electronic structure and the relative strength of the competing magnetic exchange constants. Here, we report a comparative pressure-dependent theoretical and experimental study of the electronic structure and exchange interactions of two-dimensional ferromagnets CrBr 3 and Cr 2 Ge 2 Te 6 . While CrBr 3 is found to be a Mott–Hubbard-like insulator, Cr 2 Ge 2 Te 6 shows a charge-transfer character due to the broader character of the Te 5p bands at the Fermi level. This different electronic behaviour is responsible for the robust insulating state of CrBr 3 , in which the magnetic exchange constants evolve monotonically with pressure, and the proximity to a metal–insulator transition predicted for Cr 2 Ge 2 Te 6 , which causes a non-monotonic evolution of its magnetic ordering temperature. We provide a microscopic understanding for the pressure evolution of the magnetic properties of the two systems.