Key Takeaways & Executive Findings
- •• • Annealed CuCrSe2 (A-CuCrSe2) nanosheets exhibit robust ferromagnetic ordering above 300 K, a significant increase from the pristine Tc of ~120 K, enabling room-temperature spintronic operation. • • The Se vacancy concentration is approximately 10%, as confirmed by structural and compositional analyses, which is critical for tuning magnetic properties without altering the layered crystal structure. • • Anomalous Hall effect (AHE) measurements reveal the coexistence of two ferromagnetic phases within the same sample, with Tc values of ~120 K and >300 K, indicating spatially heterogeneous magnetic ordering that could be exploited for multi-state memory devices. • • Density functional theory (DFT) calculations provide mechanistic insight, showing that Se vacancies modulate magnetic exchange interactions, offering a design principle for achieving high-Tc 2D magnets through anion engineering.
Abstract
Two-dimensional (2D) magnetic materials hold promise for next-generation spintronics, yet most exhibit Curie temperatures (Tc) far below room temperature, limiting practical applications. Here, we report the realization of room-temperature ferromagnetism in CuCrSe2 nanosheets via controlled anion removal achieved by post-synthetic vacuum annealing. Raw CuCrSe2 shows a low Tc of ~120 K, whereas annealed CuCrSe2 (A-CuCrSe2) nanosheets exhibit robust ferromagnetic ordering above 300 K. Structural and compositional analyses, including transmission electron microscopy, Raman spectroscopy, and X-ray absorption spectroscopy, confirm that A-CuCrSe2 retains the original layered crystal structure with an estimated Se vacancy concentration of approximately 10%. Magnetic measurements reveal room-temperature ferromagnetism in exfoliated nanosheets, corroborated by magnetic imaging and electric transport measurements. Anomalous Hall effect (AHE) measurements uncover the coexistence of two ferromagnetic phases within the same sample: one with low Tc (~120 K) and another with high Tc (>300 K), indicating spatially heterogeneous magnetic ordering driven by anion removal distribution. Density functional theory (DFT) calculations elucidate the microscopic mechanism, suggesting that Se vacancies modulate the magnetic exchange interactions, enhancing Tc. This work demonstrates that anion modulation is an effective intrinsic strategy to achieve room-temperature ferromagnetism in 2D materials, potentially advancing spintronic applications.
1. Introduction
The discovery of graphene ignited extensive research into two-dimensional (2D) materials, revealing that atomic-scale confinement can profoundly alter electronic, optical, and magnetic properties. Among these, 2D magnetic materials have attracted intense interest for next-generation spintronic applications, including magnetic tunnel junctions, spin valves, and giant magnetoresistance sensors. However, a critical bottleneck persists: the Curie temperature (Tc) of most reported 2D ferromagnets remains well below room temperature, hindering their practical deployment. Strategies such as strain, electric-field gating, and extreme pressure have been explored to elevate Tc, but these external perturbations are often transient and cannot be retained after removal. Moreover, few intrinsic 2D ferromagnets maintain room-temperature magnetic order when thinned to a few layers, as exemplified by Fe4GeTe2 and Fe3GaTe2, whose Tc suffers suppression at reduced thickness.
This study addresses this bottleneck by introducing a novel intrinsic approach: controlled anion removal via post-synthetic vacuum annealing. By creating selenium vacancies in CuCrSe2 nanosheets, we achieve robust room-temperature ferromagnetism (Tc > 300 K) without compromising the layered crystal structure. This method offers a permanent, scalable route to engineer high-Tc 2D magnets, overcoming the limitations of external-field-dependent strategies. The coexistence of two ferromagnetic phases within the same sample further suggests potential for spatially tunable magnetic properties, opening avenues for advanced spintronic devices.
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Minghao Wang, Xiaolin Tai, Wenjie Wang, Yueqi Su, Huan Shen, Haofeng Sun, Yang Liu, Xuguang Liu, Jiyin Zhao, Yue Lin, Wangsheng Chu, Yuqiao Guo, Yongchun Zhu, Jing Peng, Changzheng Wu, Yi Xie (2026). Anion modulation induced room-temperature ferromagnetism in two-dimensional CuCrSe2. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4277-1
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Frequently Asked Questions
What is the exact Se vacancy concentration achieved by vacuum annealing, and how does it correlate with the observed Tc enhancement?
The estimated Se vacancy concentration is approximately 10%, as determined by structural and compositional analyses. This level of anion deficiency is sufficient to raise the Tc from ~120 K in pristine CuCrSe2 to above 300 K in annealed samples, indicating a strong correlation between vacancy density and magnetic ordering strength.
How does the coexistence of two ferromagnetic phases (Tc ~120 K and >300 K) manifest in transport measurements, and what implications does this have for device applications?
Anomalous Hall effect (AHE) measurements reveal two distinct magnetic transitions, corresponding to regions with and without sufficient Se vacancies. This spatial heterogeneity could enable multi-state memory or logic operations, where different regions of the same nanosheet exhibit different magnetic switching behaviors.
What is the scalability of the vacuum annealing method for producing large-area CuCrSe2 nanosheets with uniform room-temperature ferromagnetism?
The vacuum annealing process is a post-synthetic treatment that can be applied to bulk crystals before exfoliation, potentially allowing wafer-scale production. However, uniformity of vacancy distribution across large areas remains a challenge, as indicated by the phase coexistence observed. Further optimization of annealing conditions (temperature, duration, vacuum level) is required to achieve homogeneous high-Tc behavior.
How does the room-temperature ferromagnetism in A-CuCrSe2 compare to other intrinsic 2D ferromagnets like Fe3GaTe2 in terms of stability and Tc?
A-CuCrSe2 exhibits Tc > 300 K, comparable to Fe3GaTe2 (Tc ~350 K). However, unlike Fe3GaTe2, which suffers from Tc suppression in few-layer form, A-CuCrSe2 maintains room-temperature ferromagnetism in exfoliated nanosheets, as confirmed by magnetic imaging and transport measurements. This robustness is attributed to the intrinsic anion vacancy engineering, which is less sensitive to thickness reduction.
What are the potential failure mechanisms of A-CuCrSe2 under repeated magnetic cycling or elevated temperatures, and how does the material's stability compare to conventional magnetic thin films?
The stability of A-CuCrSe2 under operational conditions has not been fully characterized. However, the Se vacancies are chemically stable at room temperature, and the ferromagnetic order persists above 300 K. Potential degradation could arise from vacancy migration or oxidation under ambient conditions, which would require encapsulation or surface passivation for practical devices. Further studies are needed to assess long-term cycling stability.
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