Room-Temperature Ferromagnetism at an Oxide-Nitride Interface

Growth of 2D Cr2 O3 -CrN Mosaic Heterostructures with Tunable Room-Temperature Ferromagnetism

2D magnets have generated much attention due to their potential for spintronic devices. Heterostructures of 2D magnets are interesting platforms for exploring physical phenomena and applications. However, the controlled growth of 2D room-temperature ferromagnetic heterostructures is challenging. Here, one-pot chemical vapor deposition growth of stable 2D Cr2 O3 -CrN mosaic heterostructures (MHs) is reported with a controlled ratio of components that possess robust room-temperature ferromagnetism. The 2D MHs consist of Cr2 O3 flakes with embedded CrN subdomains and the CrN:Cr2 O3 ratio can be tuned from 0% to 100% during growth. By changing the CrN:Cr2 O3 ratio, the ferromagnetism of the MHs (e.g., saturation magnetization, coercive field), which originates from the interfacial coupling between Cr2 O3 and CrN, can be controlled. Importantly, the obtained Cr2 O3 -CrN MHs are stable in air at elevated temperatures and have robust ferromagnetism with Curie temperature >400 K. This work presents a facile method for fabricating 2D MHs with tunable magnetism which will benefit high-temperature spintronics.

Interfacial interaction and intense interfacial ultraviolet light emission at an incoherent interface

Incoherent interfaces with large mismatches usually exhibit very weak interfacial interactions so that they rarely generate intriguing interfacial properties. Here we demonstrate unexpected strong interfacial interactions at the incoherent AlN/Al₂O₃ (0001) interface with a large mismatch by combining transmission electron microscopy, first-principles calculations, and cathodoluminescence spectroscopy. It is revealed that strong interfacial interactions have significantly tailored the interfacial atomic structure and electronic properties. Misfit dislocation networks and stacking faults are formed at this interface, which is rarely observed at other incoherent interfaces. The band gap of the interface reduces significantly to ~ 3.9 eV due to the competition between the elongated Al-N and Al-O bonds across the interface. Thus this incoherent interface can generate a very strong interfacial ultraviolet light emission. Our findings suggest that incoherent interfaces can exhibit strong interfacial interactions and unique interfacial properties, thereby opening an avenue for the development of related heterojunction materials and devices.

Heteroepitaxy of 2D CuCr2 Te4 with Robust Room-temperature Ferromagnetism

Magnetic materials in 2D have attracted widespread attention for their intriguing magnetic properties. 2D magnetic heterostructures can provide unprecedented opportunities for exploring fundamental physics and novel spintronic devices. Here, the heteroepitaxial growth of ferromagnetic CuCr₂ Te₄ nanosheets is reported on Cr₂ Te₃ and mica by chemical vapor deposition. Magneto-optical Kerr effect measurements reveal the thickness-dependent ferromagnetism of CuCr₂ Te₄ nanosheets on mica, where a decrease of Curie temperature (T_C ) from 320 to 260 K and an enhancement of perpendicular magnetic anisotropy with reducing thickness are observed. Moreover, lattice-matched heteroepitaxial ultrathin CuCr₂ Te₄ on Cr₂ Te₃ exhibits an enhanced robust ferromagnetism with T_C up to 340 K due to the interfacial charge transfer. Stripe-type magnetic domains and single magnetic domain are discovered in this heterostructure with different thicknesses. The work provides a way to construct robust room-temperature 2D magnetic heterostructures for functional spintronic devices.

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 Fe₃ N 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 Fe₃ N layer with a thickness down to 2 u.c. (≈8 Å). The MR exhibits a strong in-plane anisotropy; meanwhile, the anomalous Hall resistivity reverses its sign when the Fe₃ N layer thickness exceeds 5 u.c. Furthermore, a sizable exchange bias is observed at the interfaces between a ferromagnetic Fe₃ N 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.