Ising-Type Magnetic Ordering in Atomically Thin FePS3 (1608.04169v2)

Abstract: Magnetism in two-dimensional materials is not only of fundamental scientific interest but also a promising candidate for numerous applications. However, studies so far, especially the experimental ones, have been mostly limited to the magnetism arising from defects, vacancies, edges or chemical dopants which are all extrinsic effects. Here, we report on the observation of intrinsic antiferromagnetic ordering in the two-dimensional limit. By monitoring the Raman peaks that arise from zone folding due to antiferromagnetic ordering at the transition temperature, we demonstrate that FePS3 exhibits an Ising-type antiferromagnetic ordering down to the monolayer limit, in good agreement with the Onsager solution for two-dimensional order-disorder transition. The transition temperature remains almost independent of the thickness from bulk to the monolayer limit with TN ~118 K, indicating that the weak interlayer interaction has little effect on the antiferromagnetic ordering.

• The paper demonstrates that FePS3 exhibits intrinsic Ising-type antiferromagnetic ordering down to a monolayer with a Néel temperature of approximately 118 K.
• It employs polarized Raman spectroscopy to capture dramatic changes in Raman-active modes, providing clear evidence of magnetic spin ordering.
• The findings imply that weak interlayer interactions preserve stable magnetic properties in monolayer FePS3, promising advances in 2D spintronic technologies.

Antiferromagnetic Ordering in Two-Dimensional FePS$_3$

This paper presents an insightful investigation into the intrinsic antiferromagnetic ordering of iron phosphorus trisulfide (FePS$_3$) down to the monolayer limit utilizing Raman spectroscopy, offering a significant contribution to the field of low-dimensional magnetism. The research reveals that FePS$_3$ manifests Ising-type antiferromagnetic ordering, a noteworthy finding that suggests the Néel temperature ($T_N \approx 118 \, \text{K}$) remains effectively invariant from bulk to monolayer thickness. This indicates that weak interlayer interactions exert minimal influence on the antiferromagnetic ordering, diverging from many known magnetic systems where such interplays significantly affect magnetic properties as dimensionality reduces.

A critical examination of FePS$_3$ reveals that its monoclinic structure, comprised of a unique honeycomb lattice of transition metal (TM) atoms surrounded by sulfur atoms and phosphorus dumbbells, demonstrates robust van der Waals characteristics that enable exfoliation to a monolayer state. In FePS$_3$, the Ising nature of the transition is corroborated by dramatic modifications within its Raman spectral data due to spin ordering. Specifically, the material exhibits zone folding in the Raman-active modes, as a direct result of antiferromagnetic ordering, thereby corroborating theoretical predictions regarding long-range order in two-dimensional Ising systems.

The methodology entails using polarized Raman spectroscopy to observe magnetic transitions, offering a non-destructive approach to characterizing two-dimensional crystals. This technique effectively captures changes in the molecular vibrations, notably in modes involving transition metal atoms, as the FePS$_3$ undergoes magnetic transitions across varying temperatures. Notable transformations in these Raman peaks, which become more pronounced at reduced temperatures, provide indirect yet robust evidence of the intrinsic antiferromagnetic ordering within sole monolayers.

The authors argue that their findings represent a rare direct observation of antiferromagnetic order in a monolayer 2D material, a phenomenon predicted theoretically yet empirically elusive in prior studies. These results imply that FePS$_3$ behaves as a two-dimensional antiferromagnet close to an Ising anisotropic Heisenberg model. The persistent transition temperature across different sample thicknesses suggests potential for this material in the vertical integration of 2D devices without significant changes in their magnetic properties due to layer stacking effects.

This work provides a comprehensive means for exploring intrinsic magnetism in two-dimensional materials, which could open avenues for the development of next-generation data storage devices, spintronic applications, and quantum computing components where magnetic ground state manipulation at reduced dimensions is critical. Moreover, the encapsulation of magnetic properties in the absence of interlayer interactions could facilitate standalone monolayer systems with predictable and robust magnetic behavior.

Future research directions stemming from this paper could encompass exploring other transition metal phosphorus trichalcogenides (TMPS$_3$) for similar 2D magnetic properties, developing theoretical models encapsulating the specific spin dynamics observed, or crafting device architectures that capitalize on the robust magnetism in FePS$_3$ and akin materials. Furthermore, extending these investigations into ambiently stable and ambiently accessible derivatives of FePS$_3$ could potentially bridge the gap between theoretical magnetic properties and practical technological adoption.