Prediction and observation of defect-induced room-temperature ferromagnetism in halide perovskites

The possibility to induce a macroscopic magnetic moment in lead halide perovskites(LHPs),combined with their excellent optoelectronic properties,is of fundamental interest and has promising spintronic applications.However,these possibilities remain an open question in both theory and experiment.Here,theoretical and experimental studies are performed to explore ferromagnetic states in LHPs originated from lattice defects.First-principle calculations reveal that shallow-level Br vacancies in defective CsPbBr3 can produce spin-splitting states and the coupling between them leads to a ferromagnetic ground state.Experimentally,ferromagnetism at 300 K is observed in room-temperature synthesized CsPbBr3 nanocrystals,but is not observed in hot-injection prepared CsPbBr3 quantum dots and in CsPbBr3 single crystals,highlighting the significance played by vacancy defects.Furthermore,the ferromagnetism in the CsPbBr3 nanocrystals can be enhanced fourfold with Ni2+ion dopants,due to enhancement of the exchange coupling between magnetic polarons.Room-temperature ferromagnetism is also observed in other LHPs,which suggests that vacancy-induced ferromagnetism may be a universal feature of solution-processed LHPs,which is useful for future spintronic devices.

Facet-induced coordination competition for highly ordered CsPbBr_(3) nanoplatelets with strong polarized emission

Controllable anisotropic growth of perovskite nanocrystals(NCs)is challenging since it is difficult to separate the nucleation and growth processes.Here,a two-step nucleation strategy is proposed to control the binding interaction between surface ligands and NCs,resulting in facet-induced coordination competition.Oleic acid as surface activated ligand leads to the formation of defective lead bromine octahedron,and the binding interaction between 4-dodecylbenzenesulfonic acid and lead atoms promotes the formation of two kinds of binding interactions.Based on this strategy,the anisotropic growth of CsPbBr_(3) nanoplatelet(NPLs)with adjusted length from 11.4 to 24 nm,and the evolution of NPLs from stacked to tongue-shaped have been realized.Elemental line scan reveals the sulfur atoms mainly distribute at the edge of NPLs.Furthermore,binding energy calculation and experimental results illustrate the coordination competition of different binding interaction on specific facets induces the anisotropic growth of NPLs.Importantly,strong emission anisotropy of highly ordered NPLs with polarization ratio up to 0.58 is illustrated.This work not only deepens our understanding of the controllable synthesis of perovskite NCs,but also provides a reference for the regulation of light emitting diode and soler cells.