Designing ferromagnetic polar half-metals in short-period perovskite nickelates

ABO3 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 LnNiO3/CaNiO3 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-3d’s are interacting antiferromagnetically with O-2p. We explain that the origin of observed half metallicity and ferromagnetism is due to strong hybridization between Ni-3d and O-2p near the Fermi level and double exchange mechanism, respectively.