Emergent Magnetic States and Tunable Exchange Bias at 3d Nitride Heterointerfaces

Interfacial magnetism stimulates the discovery of giant magnetoresistance (MR) and spin-orbital coupling across the heterointerfaces, facilitating the intimate correlation between spin transport and complex magnetic structures. Over decades, functional heterointerfaces composed of nitrides have seldom been explored due to the difficulty in synthesizing high-quality nitride films with correct compositions. Here, the fabrication of single-crystalline ferromagnetic Fe3N thin films with precisely controlled thicknesses is reported. As film thickness decreases, the magnetization dramatically deteriorates, and the electronic state changes from metallic to insulating. Strikingly, the high-temperature ferromagnetism is maintained in a Fe3N layer with a thickness down to 2 u.c. (approximate to 8 angstrom). The MR exhibits a strong in-plane anisotropy; meanwhile, the anomalous Hall resistivity reverses its sign when the Fe3N layer thickness exceeds 5 u.c. Furthermore, a sizable exchange bias is observed at the interfaces between a ferromagnetic Fe3N and an antiferromagnetic CrN. The exchange bias field and saturation moment strongly depend on the controllable bending curvature using the cylinder diameter engineering technique, implying the tunable magnetic states under lattice deformation. This work provides a guideline for exploring functional nitride films and applying their interfacial phenomena for innovative perspectives toward practical applications.

Automated summary

By synthesizing single-crystalline and precisely controlled Fe3N thin films, this study demonstrates the maintenance of high-temperature ferromagnetism in thin Fe3N layers and reveals strong in-plane anisotropy and changing anomalous Hall resistivity. Additionally, a significant exchange bias is observed at the Fe3N and CrN interfaces. This work provides guidance for exploring functional nitride films and their potential applications.