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Classical spin liquid state in a rhombic lattice metal-organic framework
Nano Research 2024, 17 (4): 3407-3412
Published: 19 August 2023
Downloads:26

Discovering more and new geometrically frustrated systems remains an active point of inquiry in fundamental physics for the existence of unusual states of matter. Here, we report spin-liquid-like behavior in a two-dimensional (2D) rhombic lattice Fe-metal-organic framework (Fe-MOF) with frustrated antiferromagnetism. This Fe-MOF exhibits a high frustration factor f = |θCW|/TN ≥ 315, and its long-range magnetic order is suppressed down to 180 mK. Detailed theoretical calculations demonstrate strong antiferromagnetic coupling between adjacent Fe3+ ions, indicating the potential of a classical spin-liquid-like behavior. Notably, a T-linear heat capacity parameter, γ, originating from electronic contributions and with magnetic field independence up to 8 T, can be observed in the specific heat capacity measurements at low-temperature, providing further proof for the spin-liquid-like behavior. This work highlights the potential of MOF materials in geometrically frustrated systems, and will promote the research of exotic quantum physics phenomena.

Research Article Issue
Asymmetrical π back-donation of hetero-dicationic Mo4+–Mo6+ pairs for enhanced electrochemical nitrogen reduction
Nano Research 2022, 15 (4): 3010-3016
Published: 06 November 2021
Downloads:37

The breaking of nonpolar N≡N bond of dinitrogen is the biggest dilemma for electrocatalytic nitrogen reduction reaction (NRR) application, driving electron migration between catalysts and N≡N bond (termed “π back-donation” process) is crucial for attenuating interfacial energy barrier but still remains challenging. Herein, using density functional theory calculations, we revealed that constructing a unique hetero-dicationic Mo4+–Mo6+ pair could effectively activate N≡N bond with a lying-down chemisorption configuration by an asymmetrical “π back-donation” process. As a proof-of-concept demonstration, we synthesized MoO2@MoO3 heterostructure with double Mo sites (Mo4+–Mo6+), which are embedded in graphite, for electrochemical nitrogen reduction. Impressively, this hetero-dicationic Mo4+–Mo6+ pair catalysts display more excellent catalytic performance with a high NH3 yield (60.9 µg·h−1·mg−1) and Faradic efficiency (23.8%) as NRR catalysts under ambient conditions than pristine MoO2 and MoO3. Operando characterizations using synchrotron-based spectroscopic techniques identified the emergence of a key *N2Hy intermediate on Mo sites during NRR, which indicates that the Mo sites are active sites and the NRR process tends to follow an associative mechanism. This novel type of hetero-dicationic catalyst has tremendous potential as a new class of transition metal-based catalysts with promising applications in electrocatalysis and catalysts for energy conversion and storage.

Research Article Issue
Sulfur-vacancy-tunable interlayer magnetic coupling in centimeter- scale MoS2 bilayer
Nano Research 2022, 15 (2): 881-888
Published: 10 September 2021
Downloads:34

Endowing bilayer transition-metal dichalcogenides (TMDs) with tunable magnetism is significant to investigate the coupling of multiple electron degrees of freedom (DOFs). However, effectively inducing and tuning the magnetic interaction of bilayer TMDs are still challenges. Herein, we report a strategy to tune the interlayer exchange interaction of centimeter-scale MoS2 bilayer with substitutional doping of Co ion, by introducing sulfur vacancy (VS) to modulate the interlayer electronic coupling. This strategy could transform the interlayer exchange interaction from antiferromagnetism (AFM) to ferromagnetism (FM), as revealed by the magnetic measurements. Experimental characterizations and theoretical calculations indicate that the enhanced magnetization is mainly because the hybridization of Co 3d band and VS-induced impurity band alters the forms of interlayer orbital hybridizations between the partial Co atoms in upper and lower layers, and also enhances the intralayer FM. Our work paves the way for tuning the interlayer exchange interaction with defects and could be extended to other two-dimensional (2D) magnetic materials.

Research Article Issue
Ultrahigh-temperature ferromagnetism in MoS2 Moiré superlattice/graphene hybrid heterostructures
Nano Research 2021, 14 (11): 4182-4187
Published: 24 March 2021
Downloads:21

Realizing high-temperature ferromagnetism in two-dimensional (2D) semiconductor nanosheets is significant for their applications in next-generation magnetic and electronic nanodevices. Herein, this goal could be achieved on a MoS2 Moiré superlattice grown on the reduced graphene oxide (RGO) substrate by a hydrothermal approach. The as-synthesized bilayer MoS2 superlattice structure with rotating angle (ϕ = 13° ± 1°) of two hexagonal MoS2 lattices, possesses outstanding ferromagnetic property and an ultra-high Curie temperature of 990 K. The X-ray absorption near-edge structure and ultraviolet photoelectron spectroscopies combined with density functional theory calculation indicate that the covalent interactions between MoS2 Moiré superlattice and RGO substrate lead to the formation of interfacial Mo-S-C bonds and complete spin polarization of Mo 4d electrons near the Fermi level. This design could be generalized and may open up a possibility for tailoring the magnetism of other 2D materials.

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