Field-Free Exchange-Bias Reversal in a Substrate-Directed Self-Assembled 2-(1-3)-Type Ferrimagnet/Antiferromagnet Nanocomposite

Self-assembled nanocomposites typically form through the phase separation of immiscible components, yet controllable synthesis with tailored functionalities remains challenging. Here, we demonstrate a substrate-directed self-assembled 2-(1-3)-structured nanocomposite via topotactic phase separation, preserving the crystallographic orientation from the substrate. It comprises a horizontal antiferromagnetic (AFM) rocksalt layer (2) at the substrate and vertical rocksalt nanopillars (1) embedded in a ferrimagnetic (FiM) spinel matrix (3). The nanopillars arise from kinetic trapping of late-arriving rocksalt species unable to diffuse through the growing spinel layer, forming “frozen diffusion channels” under continuous pulsed laser deposition. Importantly, the comparable magnitudes of AFM anisotropy and AFM-FiM interfacial exchange coupling enable two phenomena: switching between coercivity enhancement and exchange bias regimes, and field-free manipulation of AFM order. This approach offers precise control of magnetic interactions in self-assembled nanocomposites for advanced spintronic applications.