Modulation of Magnetic Exchange Coupling via Constructing Bi- or Multimagnetic Heterointerfaces

How to resolve contradictions between the nanoscale size and high saturation magnetization (M s) remains one of the scientific challenges in nanoscale magnetism as the theoretical optimal M s of nanocrystals is compromised by the surface spin disorder. Here, we proposed a novel nanotechnology solution, heterointerface constructions of exchange-coupling core–shell nanocrystals, to rearrange the surface spin for the enhancement of M s of nanomagnetic materials. As a demonstration of this principle, single-interface coupling FePt@Fe3‑δO4 core/shell nanocrystals and multi-interface coupling FePt@Fe3‑δO4@MFe2O4 (M = Mn or Co) core/shell/shell nanocrystals were synthesized. The simulated and experimental results demonstrated that constructing coupling heterointerfaces orientates the overall magnetic moment, ultimately enhancing the M s of nanomagnetic materials. Moreover, this work first demonstrated that the origin of coupling heterointerfaces arose from mismatched lattices rather than chemical composition mismatch at the core–shell interfaces, thus providing both a solution to unite different mechanisms and an explanation to explain the exchange coupling at heterointerfaces.