Graphene-mediated ferromagnetic coupling in the nickel nano-islands/graphene hybrid

Air-Stable Wafer-Scale Ferromagnetic Metallo-Carbon Nitride Monolayer

The pursuit of robust, long-range magnetic ordering in two-dimensional (2D) materials holds immense promise for driving technological advances. However, achieving this goal remains a grand challenge due to enhanced quantum and thermal fluctuations as well as chemical instability in the 2D limit. While magnetic ordering has been realized in atomically thin flakes of transition metal chalcogenides and metal halides, these materials often suffer from air instability. In contrast, 2D carbon-based materials are stable enough, yet the challenge lies in creating a high density of local magnetic moments and controlling their long-range magnetic ordering. Here, we report a novel wafer-scale synthesis of an air-stable metallo-carbon nitride monolayer (MCN, denoted as MN4/CNx), featuring ultradense single magnetic atoms and exhibiting robust room-temperature ferromagnetism. Under low-pressure chemical vapor deposition conditions, thermal dehydrogenation and polymerization of metal phthalocyanine (MPc) on copper foil at elevated temperature generate a substantial number of nitrogen coordination sites for anchoring magnetic single atoms in monolayer MN4/CNx (where M = Fe, Co, and Ni). The incorporation of densely populating MN4 sites into monolayer MCN networks leads to robust ferromagnetism up to room temperature, enabling the observation of anomalous Hall effects with excellent chemical stability. Detailed electronic structure calculations indicate that the presence of high-density metal sites results in the emergence of spin-split d-bands near the Fermi level, causing a favorable long-range ferromagnetic exchange coupling through direct exchange interactions. Our work demonstrates a novel synthesis approach for wafer-scale MCN monolayers with robust room-temperature ferromagnetism and may shed light on practical electronic and spintronic applications.

Scrolling reduced graphene oxides to induce room temperature magnetism via spatial coupling of defects

Due to its intriguing features and numerous applications, graphene has garnered a lot of interest in recent years. However, it is still very difficult to create graphene-based room-temperature magnets without transition metals or rare earth elements since pristine graphene is inherently diamagnetic due to the delocalized π bonding network. Herein, room-temperature ferromagnetism with a saturation magnetization of 0.93 emu g-1 (300 K) is achieved in defect-rich-reduced graphene oxide (DR-rGO) nanoscrolls by creating a spatial coupling of defects. The experiments and DFT calculations verify that spatial coupling of defects could enhance Rudermann-Kittel-Kasuya-Yosida interactions to induce magnetism in graphene. It displays high-efficiency electromagnetic wave absorption performance with a minimal reflection loss of -62.1 dB and an effective absorption bandwidth of 7.8 GHz (3.0 mm) thanks to greatly improved magnetism. This breakthrough serves as a building block for the creation of room-temperature magnetic carbon materials and expands their applications in many pertinent domains.

Strain-Dependent Band Splitting and Spin-Flip Dynamics in Monolayer WS2

Triggered by the expanding demands of semiconductor devices, strain engineering of two-dimensional transition metal dichalcogenides (TMDs) has garnered considerable research interest. Through steady-state measurements, strain has been proved in terms of its modulation of electronic energy bands and optoelectronic properties in TMDs. However, the influence of strain on the spin-orbit coupling as well as its related valley excitonic dynamics remains elusive. Here, we demonstrate the effect of strain on the excitonic dynamics of monolayer WS₂ via steady-state fluorescence and transient absorption spectroscopy. Combined with theoretical calculations, we found that tensile strain can reduce the spin-splitting value of the conduction band and lead to transitions between different exciton states via spin-flip mechanism. Our findings suggest that the spin-flip process is strain-dependent, provides a reference for application of valleytronic devices, where tensile strain is usually existing during their design and fabrication.

Supercritical CO2 -induced New Chemical Bond of C-O-Si in Graphdiyne to Achieve Robust Room-Temperature Ferromagnetism

The realization of ferromagnetic ordering of two-dimensional (2D) carbon material graphdiyne (GDY) has attracted great attention due to its promising application in spin semiconductor devices. However, the absence of localized spins makes the pristine GDY intrinsically nonferromagnetic. Herein, we report the realization of robust room-temperature (RT) ferromagnetism (FM) with Curie temperature (T_C ) up to 325 K for GDY Nanosheets (GDYNs) by supercritical CO₂ (SC CO₂ ). Experimental and theoretical calculations reveal that the new chemical bond of C-O-Si can be formed because of the unique effect of SC CO₂ , which help to enhance the charge transfer and generates long-range ferromagnetic order. The RT saturation magnetization (M_S ) reaches 1.125 emu/g, which is much higher than that of carbon-based materials reported up to now. Meanwhile, by changing the conditions of SC CO₂ such as pressure, ferromagnetic responses can be manipulated, which is great for potential spintronics applications of GDY.

Spin-Dependent Transport at 2D Solids: From Nonmagnetic Layers to Ferromagnetic van der Waals Structures

Spintronics is a promising alternative to the conventional silicon transistor-based electronics that are gradually approaching their physical limitations. Ultrathin two-dimensional van der Waals (vdW) materials (2D materials) with controllable spin degrees of freedom are recognized as extremely promising spintronic materials in architectures for the post-Moore era. In this Perspective, we review recent progress on spin-dependent transport behaviors (SDTBs) confined at the 2D scale, which are the mainstream paradigms for spintronic devices. We first present the mechanism and the key factors of SDTBs in 2D nonmagnetic materials-based hybrid devices. Then, some chemical modulation strategies for inducing short-range magnetic order and magneto-electric performance into 2D nonmagnetic materials are discussed. Furthermore, we concentrate on introducing intriguing SDTBs in 2D long-range ferromagnetic materials-based vdW devices. Finally, we highlight the current challenges in the study of spin-dependent transport of 2D modified materials and 2D material-based spintronic devices, in the hope of accelerating their applications.