Multiferroicity in a Two-Dimensional Non-van der Waals Crystal of AgCr₂X₄ (X = S or Se)

Abstract

Two-dimensional (2D) intrinsic multiferroics have long been pursued not only for their potential technological applications but also as model systems for studying emergent quantum phenomena and coupling mechanisms between various order parameters in low-dimensional space. However, the realization of 2D multiferroics is still a challenge. In this paper, we reveal that 2D AgCr2X4 (X = S or Se) crystals, which have been synthesized from the non-van der Waals (non-vdW) AgCrX2 bulk phase, are type I half-metallic/metallic multiferroics in which ferroelectricity and ferromagnetism coexist. The off-centering displacement of the Ag ion introduces out-of-plane polarization, and the magnetism originates from the interactions between Cr atoms. Remarkably, AgCr2Se4 shows topologically nontrivial spin textures, such as Meron pairs and Néel-type skyrmions, under suitable temperatures and magnetic fields. Our findings demonstrate that 2D multiferroics can be achieved from non-vdW materials and in turn open a new avenue for 2D multiferroics.

Adsorption Tuning of Polarity and Magnetism in AgCr2S4 Monolayer

“…The local magnetic moment increases with the increase in Ueff, reaching 2.86 µB/Cr at 0.6 eV, which is consistent with previously reported value [22]. Moreover, the optimized lattice constants (a = 13.83 Å, b = 3.54 Å, and c = 7.13 Å) are in good agreement with the experimental data [22,24]. Therefore, it will be adopted in the following calculations by default.…”

“…Recently, the monolayer AgCr 2 S 4 , consisting of a single Ag layer sandwiched between two CrS 2 layers, was successfully exfoliated from AgCrS 2 bulk [17]. Interest has been aroused [23,24], mainly focusing on the magnetic and ferroelectric properties of single-layer AgCr 2 S 4 . However, the specific structure of the monolayer, the possible surface adsorption after peeling, and their effects on material properties have not been well explored.…”

The effect of switchable electronic polarization states on the electronic properties of two-dimensional multiferroic TMBr2/Ga2SSe2 (TM = V–Ni) heterostructures

“…[2][3][4][5] 2D AgCr 2 X 4 (X = S or Se) monolayers are theoretically explored to be type I half-metallic/ metallic multiferroics with topologically nontrivial spin textures. 6 2D CrPSe 3 is found to be a MF with a tunable magnetic ground state due to the switchable FE state induced by an out-of-plane electric field. 7 However, the fabrication of pristine MF materials is a great challenge due to the different origins of magnetism and electric polarization, namely, FE prefers fully occupied d orbitals while FM prefers partially occupied d orbitals.…”

Intrinsic single-layer multiferroics in transition-metal-decorated chromium trihalides

“…The mutually exclusive requirements for the fully electronic occupation of the outer valence shell make it particularly challenging to achieve FM and FE simultaneously in the bulk material. [5][6][7][8][9][10][11][12][13][14][15][16][17] 2D multiferroic semiconductors with atomic thickness have received considerable attention due to their ability to overcome these mutually exclusive requirement. 18 The out-of-plane ferroelectricity in 2D magnetic materials is generally considered to decrease the depolarization eld.…”