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ABO 3 perovskites oxides show fascinating functional properties, including ferroelectricity, magnetism, metal-to-insulator transition, half metallicity, polar metallic phase, etc. In particular, rare earth nickelates and alkaline earth nickelates within the orthorhombic crystal structures show an insulator–metal transition (IMT) and half-metallic (HM) nature respectively. Here, we report a series of ferromagnetic polar half metals by constructing LnNiO 3 /CaNiO 3 short period 1/1 superlattices (SLs) with Ln = La, Nd, Gd, Dy, Tm, and Lu within an orthorhombic phase. The polar distortion is induced by a hybrid-improper ferroelectric mechanism i.e., by constructing Ln/Ca layer-ordering. The system shows a ferromagnetic Ni-Ni interaction, whereas Ni-3 d 's are interacting antiferromagnetically with O-2 p. We explain that the origin of observed half metallicity and ferromagnetism is due to strong hybridization between Ni-3 d and O-2 p near the Fermi level and double exchange mechanism, respectively. • Ferromagnetic polar half-metals within LnNiO 3 /CaNiO 3 • Large spin polarization is expected. • Hole mediated double exchange mechanism drives the ferromagnetic ordering. • The systems exhibit polar nature through hybrid improper ferroelectric mechanism. • These systems are metallic due to strong hybridization between Ni-3 d and O-2 p. [ABSTRACT FROM AUTHOR]

Starting from a room temperature parent La 2 MnNiO 6 double perovskite as a prototype example, we ventured ferroelectricity and metal–insulator transition in the AA ′ BB ′ O 6 double perovskites. Using first-principles density functional calculations guided by symmetry, we have shown that by appropriate A-site substitution i.e., by forming AA ′ combinations, La 2 MnNiO 6 within Mn and Ni in rock-salt ordering can be transformed into both ferroelectric insulating or polar metallic phase. We found that the charge difference between the cations and the radius mismatch between A and A ′ are the key factors for deciding a particular ordering. The layered ordering becomes more stable when both charge difference and radius mismatch are large. The energy gain is more pronounced when the charge difference at the A-site is large. Further, we have identified and discussed the key structural distortions responsible for driving functional properties into the system. Our proposed mechanism is valid for other similar A 2 BB ′ O 6 systems within 3 d -3 d double perovskites architecture with B and B ′ sublattices in the rock-salt ordering. • A-site cation ordered double perovskites are not common in the literature. • A-site cation ordered double perovskites are designed. • Layered double perovskites are established multiferroics. • The additional carrier(s) can lead the systems to a metal–insulator transition. [ABSTRACT FROM AUTHOR]

Two-dimensional ferromagnetic materials are potential candidates that can be integrated with the current nanoelectronic and spintronic device architecture. The latest trends in designing spintronic devices are mainly based on two-dimensional (2D) inorganic compounds. Here, we present a study based on first-principles density functional calculations where we design a 2D ferromagnetic material within the family of metal − organic frameworks. Starting from the inorganic CrI 3 compound, we demonstrate that a chromium-based metal − organic compound i.e. Cr(COOH) 3 can be stabilized in a ferromagnetic state compared to the other possible anti-ferromagnetic states. The proposed structure of Cr(COOH) 3 is found to be thermodynamically stable, but its dynamic stability could not be verified because of complexity into the structure. The lowest energy magnetic configuration of pure Cr(COOH) 3 turns out to be antiferromagnetic. However, our calculations suggest that the presence of positively charged Cr-vacancy defects can stabilize the ferromagnetic state over antiferromagnetic orderings. The presence of delocalized holes is found to be responsible for favoring the ferromagnetic ordering. • The 2D MOF structure derived from CrI 3 structure is thermodynamically stable. • In its pristine form, it is an antiferromagnetic insulator. • Cr vacancy defects can stabilize the ferromagnetic ground state over antiferromagnetic orderings. • Cr-vacancy induces ferromagnetic ordering. [ABSTRACT FROM AUTHOR]

• DFNA molecular crystal is studied with DFT techniques. • Strain-engineering is implemented for structural properties. • Also, we investigated electronic properties upon strain. • The DFNA crystal is found to be a structural buffer in nature. We use first-principles density functional theory (DFT) calculations to investigate the effects of strain on the properties of elastic organic 2, 6-dichlorobenzylidene-4-fluoro-3-nitroaniline (DFNA) crystal. Our results from DFT calculations are in agreement with the recent experimental results of elastic DFNA crystal. The systematic calculations on the criss-cross arrangement of the crystal show that π ⋯ π stacking along with weak and dispersive non-covalent interactions play a pivotal role in stabilizing the structure. We consider the following interactions, namely type-I Cl ⋯ Cl interaction, type-II F ⋯ Cl interaction, and C–H ⋯ O interaction, and investigate how the interactions are tuned subject to strain. Also, we investigate the modification of the π ⋯ π stacking along crystallographic a axis in the criss-cross packing upon the strain. [ABSTRACT FROM AUTHOR]