Theoretical Insights and Experimental Studies of the New Layered Tellurides EuRECuTe₃ with RE = Nd, Sm, Tb and Dy

Abstract

Single crystals of the layered EuRECuTe₃ series with RE = Nd, Sm, Tb and Dy are obtained for the first time, completing the series of studies on quaternary tellurides synthesized using the halide flux method. These compounds crystallize in the orthorhombic space group Pnma (no. 62) with unit cell parameters ranging from a = 11.5634(7) Å, b = 4.3792(3) Å and c = 14.3781(9) Å for EuNdCuTe₃ to a = 11.2695(7) Å, b = 4.3178(3) Å and c = 14.3304(9) Å for EuDyCuTe₃. The influence of prismatic polyhedra [EuTe₆₊₁]⁷⁻ structural units on the stabilization of 3d framework composed by 2d layered fragments [RECuTe₃]²⁻, which have a key role in the interlayer interaction, is established. A comparative analysis of structural and magnetic properties dependence on the rare-earth element radius r_i(RE³⁺) in the EuRECuTe₃ series (RE = Sc, Y, Nd–Lu) is carried out. The structural contraction, including decrease in degree of tetrahedral polyhedra distortion, bond lengths shortening and unit cell volume shrinking with increasing r_i(RE³⁺), is established. It is shown that the structural alternation leads to transition from ferromagnetic to ferrimagnetic ordering. It was established that changes in the cationic sublattice have a more significant impact on structural transitions in the series of quaternary tellurides than changes in the anionic sublattice. The electronic structure and elastic and dynamic properties were estimated using ab initio calculations. The exfoliation energy for each compound is obtained by estimation of monolayer ground state energy as a result of structure relaxation. The symmetry and structural properties of monolayer EuRECuTe₃ (RE = Nd, Sm, Tb, Dy) compound are established and the orthorhombic symmetry is obtained with layer group pm2_1b.

1. Introduction

Layered materials based on metal chalcogenides have great potential for use in optoelectronics, photonics, flexible electronics, highly sensitive sensor systems, catalysis, as well as in energy storage and conversion devices [1,2,3,4,5]. Layered chalcogenide structures possess various properties depending on their composition and can be semiconductors, semimetals, true metals, and superconductors [6]. Their properties are also regulated by the crystal structure, the number, and the stacking sequence of layers in the crystals [6]. Due to the development of efficient exfoliation methods, it is becoming increasingly possible to experimentally obtain two-dimensional crystals from almost any layered material known in chemistry [7].

Experimentally obtained quaternary copper chalcogenides with the composition MRECuCh₃ (M = Eu [8,9,10,11,12,13,14,15,16], Ba [17,18,19,20,21,22,23,24,25,26,27,28], Sr [29,30,31], Pb [32,33,34,35]; Ch = S, Se, Te; RE = Sc, Y, La–Nd, Sm–Lu) crystallize in four structural types: KZrCuS₃, Eu₂CuS₃, Ba₂MnS₃ and BaLaCuS₃. The decrease in the symmetry of the crystal structure and the sequential change in structural types are caused by the increasing distortion of the parallel two-dimensional [RECuCh₃]²⁻ layers in the KZrCuS₃ → Eu₂CuS₃ → Ba₂MnS₃ series [21]. When the distortion becomes so strong that the layers connect with each other, a three-dimensional channel structure of the BaLaCuS₃ type is formed [21,36,37]. The formation of 2D layers contributes to improved electrical transport characteristics in multilayer solar cells [25,27,28,38,39]. In heterometallic chalcogenides, substantial exfoliation energy is observed, since interlayer interaction is governed by both van der Waals and covalent forces [40]. This indicates the promise of using alternative methods for obtaining monolayer structures compared to traditional approaches: pulsed laser deposition [41], chemical vapor deposition [42], physical vapor deposition [43] and molecular beam epitaxy [44]. In these structures, one-dimensional chains of acentric tetrahedra are also formed, indicating their potential use as photonic materials for nonlinear optical devices [26]. Incorporating magnetic cations Eu²⁺ and RE³⁺ into heterometallic chalcogenides, as well as using the chalcogen with the largest radius, simultaneously leads to a decrease in band gap width and the emergence of magnetic properties. This opens up the possibility of creating materials that combine optimal semiconductor characteristics for photovoltaic devices and the properties of ferro- and ferrimagnetics, which are important for magnetic electronics [8,45,46].

The theoretical existence of orthorhombic compounds of the entire EuRECuTe₃ series was predicted in [39]. According to calculations, compounds with light lanthanides such as RE = La, Ce, Pr are metastable and crystallize in the BaLaCuS₃ structural type with Pnma symmetry [39]. The remaining EuRECuTe₃ (RE = Nd, Sm–Lu) representatives are stable, with most expected to form crystals of the KZrCuS₃ structural type with Cmcm symmetry [39]. To date, using the halide flux method, six quaternary europium tellurides EuRECuTe₃ (RE = Gd [47], Ho [48], Tm [48], Er [49], Lu [47], Sc [48], Y [40]) have been obtained. It has been established that these compounds have a layered structure, are ultra-narrow bandgap semiconductors [40], simultaneously exhibit soft ferromagnetic [40] or ferrimagnetic [49] properties, and are characterized by low thermal conductivity [38,39,40]. Additionally, a rearrangement of the crystal structure was found with a slight increase in temperature, and significant prospects for the synthesis of monolayer structures were demonstrated [40].

No reports exist in the available literature on the synthesis and structural analysis of tellurium-containing EuRECuTe₃ (RE = La, Ce, Pr, Nd, Sm, Tb or Dy) single crystals. The ionic radius of europium r_i(Eu²⁺) is close to that of strontium r_i(Sr²⁺) [50]. Therefore, it can be expected that europium compounds with rare-earth elements in the range from La to Dy will form the same type of crystal lattice as their strontium analogs. Experimentally, it has been established that the SrRECuTe₃ representatives with RE = Sm–Tb crystallize in the orthorhombic space group Pnma with the Eu₂CuS₃ structure type [51], which raises doubts about the conclusions in [39]. The possibility of synthesizing europium compounds with light rare-earth elements in Pnma symmetry is confirmed by studies of layered quaternary chalcogenides MRECuCh₃ (RE = La–Nd, Sm, Tb, Dy; M = Sr [21,29,30,31], Eu [8,9,12,13,14,15,16,36,37], Ba [17,22,23,24,25,26,27]; Ch = S, Se, Te).

The experimental synthesis of tellurides with light rare-earth elements will complete the cycle of research on the synthesis of europium chalcogenides by the halide flux method and will significantly expand the fundamental knowledge in the chemistry of rare-earth chalcogenides. Layered structures are of great interest for technical applications, especially in submicron electronics, as tunable materials for photovoltaic and sensor devices.

In this work, the tellurides EuRECuTe₃ (RE = Nd, Sm, Tb, Dy) were obtained for the first time, their crystal structures were refined, and their magnetic properties were studied. Dependencies of changes in structural and magnetic characteristics on the rare-earth ionic radius in the series EuRECuTe₃ (RE = Sc, Y, Nd, Sm–Lu) have been established. The results of band structure calculations, as well as elastic and dynamic properties, are presented, which help explain the reasons for changes in symmetry in the EuRECuTe₃ (RE = Sc, Y, Nd, Sm–Lu) telluride series. In addition, modeling of the monolayer exfoliation process was performed, and a theoretical analysis of its dynamic properties was carried out.

2. Materials and Methods

2.1. Materials

The elements Eu (99.99%), Nd (99.99%), Sm (99.99%), Tb (99.99%), Dy (99.99%), Te (99.9%), Ar (99.99%) as well as C₂H₂ (99.9%) and CsI (99.9%) were purchased from ChemPur (Karlsruhe, Germany), while Cu (99.999%) was obtained from Aldrich (Milwaukee, WI, USA).

2.2. Synthesis

Single crystals of the new EuRECuTe₃ members with RE = Nd, Sm, Tb and Dy were obtained using the halide flux method according to the procedure described in [40].

During synthesis, needle-like single crystals of EuRECuTe₃ (RE = Nd, Sm, Tb, Dy) with a black color and metallic luster, up to 1400 μm in length (Figure S1 in the Supplementary Materials), were obtained, with no impurity phases detected according to the powder X-ray diffraction data (Figure 1).

Attempts were also made to synthesize quaternary chalcogenides EuRECuTe₃ (RE = La, Ce, Pr, Eu), but all of these attempts were unsuccessful. A variation in temperature and time conditions of synthesis and various variations in halide flux did not lead to the formation of single crystals of the target phase EuRECuTe₃. During the synthesis of EuRECuTe₃ compounds (RE = La, Ce, Pr), inclusion of cesium from the flux (CsI) into hexagonal compounds (space group: P6₃/m) of the composition Cs_xCu_6−xRE₂Te₆ (RE = La, Ce, Pr) [52] was observed and single crystals of Cu₀.₄RETe₂ also [53]. EuTe were also present in the samples. Unfortunately, single crystals of the EuRECuTe₃ phase (RE = La, Ce, Pr) could not be detected in the obtained samples. During the synthesis of Eu²⁺Eu³⁺CuTe₃, single crystals of Cu₀.₆₆EuTe₂ and EuTe were identified among the reaction products. Single crystals of Eu²⁺Eu³⁺CuTe₃ could also not be detected, probably due to the insufficient oxidizing ability of tellurium, which prevents the oxidation reaction of europium according to the scheme Eu⁰–3e⁻ = Eu³⁺ from occurring.

2.3. X-Ray Diffraction Analysis

The single-crystals diffraction intensities of EuRECuTe₃ (RE = Nd, Sm, Tb, Dy) were obtained at room temperature 293(2) K using a κ-CCD single crystal diffractometer (Bruker AXS, Billerica, MA, USA) equipped with a CCD detector, a graphite monochromator and a Mo-K_α radiation source. The unit-cell parameters of all the studied compounds corresponded to the orthorhombic crystal system. The space group Pnma was determined based on a statistical analysis of the reflection intensities. Absorption correction was performed using the SADABS program (2008). The structure was solved by direct methods using the SHELXS program (2013), and further refinement was carried out anisotropically with SHELXL (2013) [54]. The analysis for possible missing symmetry elements was performed using the PLATON program (2009) [55]. The crystallographic data have been deposited at the Cambridge Crystallographic Data Centre and can be obtained at http://www.ccdc.cam.ac.uk/data_request/cif (accessed on 25 April 2025).

Powder diffraction data were obtained at room temperature on a Rigaku SmartLab powder diffractometer (Rigaku Corporation, Tokyo, Japan) using monochromatic Cu-K_α radiation in reflection mode.

2.4. Magnetic Measurements

The magnetic measurements were performed via the MPMS3 measurement system by Quantum Design (San Diego, CA, USA). Using a SQUID magnetometer, the temperature dependencies of the magnetic moments of the EuRECuTe₃ samples with a mass of 0.01305 g (EuNdCuTe₃), 0.01000 g (EuSmCuTe₃), 0.00984 g (EuTbCuTe₃) and 0.01304 g (EuDyCuTe₃) were measured in the temperature range from 2 to 300 K under a constant external field of 40 kA∙m⁻¹. Measurements were conducted in both FC (field-cooled) and ZFC (zero-field-cooled) modes. Another experiment consisted of measuring the dependence of the magnetic moment of the same sample stayed at constant temperature on changing the external magnetic field using a vibrating sample magnetometer. The field varied from 0 to ±4 MA∙m⁻¹ in magnitude, the temperature points were 2 and 300 K.

2.5. Spectroscopy of the Raman Scattering

Raman spectra of the single crystal samples of EuRECuTe₃ were acquired using a Horiba XploRa spectrometer (HORIBA Scientific, Kyoto, Japan). The excitation light at a wavelength of 532 nm was used. The acquisition conditions were as follows: filter-10, hole-300, slit-100, and resolution-2400.

2.6. Calculations at Framework of DFT

For the first time, a DFT study of crystals EuRECuTe₃ (RE = Nd, Sm, Gd, Tb, Dy) with hybrid functional B3LYP was carried out. The calculations were made in the MO LCAO approximation in the CRYSTAL17 program [56,57], developed for periodic structures.

We employed pseudo-potentials ECPnMWB “4f in core” for RE and Eu ions [58,59]. The outer shells of RE and Eu ions were modeled using TZVP basis sets. These pseudo-potentials combined with the basis sets for the outer shells are accessible on the website [60]. For copper and tellurium, all-electron bases available on CRYSTAL program’s website and Mike Towler’s website [61] were employed accordingly. The exponents in the eighth, ninth and tenth contractions were set to 0.3797, 0.5309 and 0.1900, respectively. At integration in the CRYSTAL code the Monkhorst–Pack method used. In our calculations, the k-point grid was chosen as 8 × 8 × 8. Two-electron integrals were computed with a precision of at least 10⁻⁸ a. u. The SCF was calculated with tolerance no less than 10⁻⁹. Phonons or elastic constants were calculated for the optimized crystal structure. Algorithms of the calculations are considered in work [62].

The most optimal for crystals with ionic or covalent chemical bond are exchange-correlation DFT functionals, which take into account the contribution of non-local exchange in the Hartree–Fock formalism. These are so-called hybrid functionals. The most well-known hybrid functional is B3LYP (20% HF exchange) [63]. The functional has been reliably tested for compounds with ionic and covalent bonds [64].

3. Results

3.1. Layered Crystal Structures of EuRECuTe₃ (RE = Nd, Sm, Tb, Dy) and Regularities in the Variation in Structural Parameters in the EuRECuTe₃ Series (RE = Nd, Sm–Lu)

According to single-crystal X-ray structural analysis, the four new members of EuRECuTe₃ with RE = Nd, Sm, Tb and Dy crystallize in the orthorhombic space group Pnma corresponding to the Eu₂CuS₃ structure type. The structural data are presented in Tables S2–S5 in the Supplementary Materials. The synthesized tellurides have the same crystal structure as the quaternary chalcogenides with the formula EuRECuSe₃ [9] and EuRECuS₃ [8,11,12,13,15,36]. The unit cell parameters determined by DFT calculations (a = 11.6190 Å, b = 4.3862 Å, c = 14.2561 Å for EuNdCuTe₃, a = 11.4632 Å, b = 4.3724 Å, c = 14.2881 Å for EuSmCuTe₃, a = 11.3644 Å, b = 4.3651 Å, c = 14.2684 Å for EuGdCuTe₃, a = 11.3192 Å, b = 4.3567 Å, c = 14.2672 Å for EuTbCuTe₃ and a = 11.2971 Å, b = 4.3504 Å, c = 14.2474 Å for EuDyCuTe₃) are in good agreement with the experimental values (Table S2 in the Supplementary Materials, Figure 2). Previously, experimental data on the crystal structure and properties for the compound EuGdCuTe₃ were presented in [47], but DFT calculations were not carried out. In this work, we have addressed this gap and performed ab initio calculations for this compound.

In the series of the quaternary tellurides EuRECuTe₃ (RE = Nd, Sm–Dy), isostructural with Eu₂CuS₃, due to the decrease in the ionic radius RE³⁺ (~7%) [50], the observed reduction in lattice parameters and unit cell volume occurs in the following ranges: a = 11.5634(7)–11.2695(7) Å, b = 4.3792(3)–4.3178(3) Å, c = 14.3781(9)–14.3304(9) Å, V = 728.08(8)–697.31(8) ų (Table S2, Figure 2). The parameter a undergoes the greatest change, decreasing by 2.5%, the parameter b by 1.4%, and the parameter c by 0.33%, with the overall unit cell volume changing by 4.3%. A decrease in the RE–Te bond distance by 3.1% was also observed, ranging from 3.1438(8)–3.045(1) Å (Table S5 in the Supplementary Materials, Figure 3), which correlates with the reduction in the RE³⁺ radius. For six bonds, d(RE–Te), the experimental values are smaller than the theoretical values (d(Nd–Te) = 3.193 Å) and d(Dy–Te) = 3.112 Å [50]. Distorted octahedra [RETe₆]⁹⁻ are formed in the structures, consisting of covalent polar bonds, forming infinite layers through edge-sharing along the b-axis (Figure 4). When forming the coordination polyhedron, Te²⁻ ligands with distances exceeding the theoretically calculated value were not considered, as they have negligible interaction forces. The deviation of the ∡(Te–RE–Te) bond angles from the theoretical octahedral value ranges from 0.04% to 3.1% (Table S5 in the Supplementary Materials). In EuNdCuTe₃, the d(Cu–Te) bond lengths range from 2.649(2) to 2.696(1) Å, while in EuDyCuTe₃ they range from 2.632(2) to 2.673(1) Å; both are shorter than the theoretical value of 2.81 Å [50]. The deviation of the ∡(Te–Cu–Te) bond angles from the theoretical tetrahedral value is 0.7–3% (Table S5 in the Supplementary Materials). To assess the degree of distortion of the [CuTe₄]⁷⁻ tetrahedra, distortion coefficients DI(Te–Cu–Te), DI(Cu–Te), and DI(Te···Te) were calculated (

Table 1. Distortion parameters for tetrahedra and octahedra in the structure of EuRECuTe₃ compounds.

Compound	Structural Type	DI(Te–Cu–Te)	DI(Cu–Te)	DI(Te···Te)	σ2
Distortion parameters for [CuTe4]7− tetrahedra
EuNdCuTe3	Eu2CuS3	0.0247	0.0473	0.0162	16.794
EuSmCuTe3	Eu2CuS3	0.0234	0.0493	0.0166	14.324
EuGdCuTe3	Eu2CuS3	0.0222	0.0511	0.0171	12.716
EuTbCuTe3	Eu2CuS3	0.0212	0.0526	0.0172	11.530
EuDyCuTe3	Eu2CuS3	0.0205	0.0539	0.0181	10.227
EuYCuTe3	Eu2CuS3	0.0208	0.0536	0.0142	9.636
EuHoCuTe3	KZrCuS3	0.0194	0.0550	0.0191	7.892
EuErCuTe3	KZrCuS3	0.0185	0.0555	0.0196	6.960
EuTmCuTe3	KZrCuS3	0.0175	0.0562	0.0203	6.207
EuLuCuTe3	KZrCuS3	0.0160	0.0576	0.0217	4.933
EuScCuTe3	KZrCuS3	0.0058	0.0687	0.0332	0.842
Distortion parameters for [RETe6]9− octahedra
EuNdCuTe3	Eu2CuS3	0.0138	0.0206	0.0094	1.826
EuSmCuTe3	Eu2CuS3	0.0110	0.0211	0.0095	1.628
EuGdCuTe3	Eu2CuS3	0.0117	0.0212	0.0151	2.013
EuTbCuTe3	Eu2CuS3	0.0135	0.0212	0.0191	2.475
EuDyCuTe3	Eu2CuS3	0.0149	0.0216	0.0227	3.011
EuYCuTe3	Eu2CuS3	0.0145	0.0177	0.0227	2.927
EuHoCuTe3	KZrCuS3	0.0153	0.0210	0.0256	3.086
EuErCuTe3	KZrCuS3	0.0175	0.0202	0.0283	3.790
EuTmCuTe3	KZrCuS3	0.0189	0.0191	0.0304	4.220
EuLuCuTe3	KZrCuS3	0.0220	0.0177	0.0349	5.404
EuScCuTe3	KZrCuS3	0.0346	0.0047	0.0593	11.325

), using the methods proposed in [65,66], and the σ² values were obtained using the methodology described in [67]. With a decrease in the ionic radius of RE³⁺ in the EuRECuTe₃ structure, the distortion of the ∡Te–Cu–Te bond angles relative to symmetric coordination decreases, and the σ² bond angle dispersion decreases (Figure 5), which results in the formation of a more regular tetrahedral structure (Table 1). The greatest distortions of polyhedra are manifested in the d(Cu–Te) distances, compared to d(Te···Te) and ∡Te–Cu–Te (Table 1). However, the decrease in the ionic radius of RE³⁺ leads to a change in the space group from the less symmetrical Pnma to the more symmetrical Cmcm in the EuRECuTe₃ series. Therefore, the distortions in the d(Cu–Te) bonds are most likely of a local nature and do not affect the overall symmetry of the structure. In contrast to the behavior of the [CuTe₄]⁷⁻ tetrahedra, the analysis of octahedral distortion parameters for the [RETe₆]⁹⁻ polyhedra reveals an opposite trend. With decreasing RE³⁺ ionic radius and the corresponding transition from Pnma to Cmcm symmetry, the bond angle variance in the [RETe₆]⁹⁻ octahedra actually increases, indicating a greater deviation from ideal geometry. This effect can be attributed to enhanced crystal-chemical compression in the more densely packed Cmcm phase, where the incorporation of smaller RE³⁺ ions leads to increased local strain and angular distortion within the octahedra. Thus, despite the higher global symmetry of the Cmcm structure, the local environment of the rare-earth cation becomes more distorted, highlighting the fact that increased structural symmetry does not necessarily result in lower polyhedral distortion for all coordination types within the lattice.

Distorted vertex-connected copper tetrahedra form chains along the b-axis, and by edge-sharing with the distorted octahedra [RETe₆]⁹⁻, they create parallel two-dimensional layers in the ab plane (Figure 4). Thus, a layered structure of the quaternary chalcogenide is formed (Figure 4). Between these parallel layers are located the seven-coordinate Eu²⁺ cations, which form chains of single-capped trigonal prisms along the b-axis, connected pairwise by faces. As the ionic radius of r_i(RE³⁺) decreases, crystallochemical compression of the parallel layers occurs, which subsequently leads to changes in the europium coordination, structure type, and space group of the compounds.

Calculation of the sum of valence forces taking into account the coordination environment showed that the oxidation states of Eu, RE, and Cu ions in the compounds EuRECuTe₃ are approximately 2, 3, and 1, respectively. The obtained values are as follows: for Eu (1.71–1.75), for RE (3.01–3.16), for Cu (1.33–1.41) (Table S6 in the Supplementary Materials).

Thus, according to previously conducted studies on tellurides [40,47,48,49] and the present work, it has been established that the compounds in the EuRECuTe₃ series (RE = Nd, Sm, Gd–Lu) crystallize in two space groups: Pnma (for RE = Nd (this work), Sm (this work), Gd [47], Tb (this work), Dy (this work), Y [40]) and Cmcm (for RE = Ho [48], Er [49], Tm [48], Lu [47], Sc [48], Y [40]), and two structural types: Eu₂CuS₃ and KZrCuS₃, respectively.

The crystal structures of the compounds in the EuRECuTe₃ series share both similarities and differences (Figure 4). Some of the similarities include the following:

✓

The Eu²⁺, RE³⁺, and Cu⁺ cations are crystallographically independent.

✓

The Cu⁺ and RE³⁺ cations in different space groups throughout the EuRECuTe₃ series form similar coordination polyhedra.

✓

In all structures of the EuRECuTe₃ series, distorted copper tetrahedra are joined via two shared vertices, forming infinite linear chains ${}_{\infty }{}^1\left\{{\left[\mathrm{Cu}{\left(\mathrm{Te}1\right)}_{1/1}^t{\left(\mathrm{Te}2\right)}_{1/1}^t{\left(\mathrm{Te}3\right)}_{2/2}^e\right]}^{5-}\right\}$ for EuRECuTe₃ (RE = Y, Nd, Sm–Dy) and ${}_{\infty }{}^1\left\{{\left[\mathrm{Cu}{\left(\mathrm{Te}1\right)}_{2/2}^e{\left(\mathrm{Te}2\right)}_{2/1}^t\right]}^{5-}\right\}$ for EuRECuTe₃ (RE = Sc, Y, Ho–Lu).

✓

In these structures, distorted [RETe₆]⁹⁻ octahedra are interconnected by shared edges and vertices, forming two-dimensional layers ${}_{\infty }{}^2\left\{{\left[{RE\left(\mathrm{Te}1\right)}_{2/2}{\left(\mathrm{Te}2\right)}_{2/2}{\left(\mathrm{Te}3\right)}_{2/2}\right]}^{3-}\right\}$ along the b-axis for RE = Y, Nd, Sm–Dy, and ${}_{\infty }{}^2\left\{{\left[RE{\left(\mathrm{Te}1\right)}_{2/2}^e{\left(\mathrm{Te}2\right)}_{4/2}^k\right]}^{-}\right\}$} along the a-axis for RE = Sc, Y, Ho–Lu.

✓

Parallel two-dimensional layers ${}_{\infty }{}^2\left\{{\left[\mathrm{Cu}RE{\mathrm{Te}}_3\right]}^{2-}\right\}$ are formed.

The differences include the following:

✓

In the compounds EuRECuTe₃ (RE = Nd–Dy), chains of copper tetrahedra [CuTe₄] are formed along the b axis, and two-dimensional layers ${}_{\infty }{}^2\left\{{\left[\mathrm{Cu}RE{\mathrm{Te}}_3\right]}^{2-}\right\}$ are formed in the ab plane. In the compounds EuRECuTe₃ (RE = Ho–Lu, Sc, Y), the formation of chains and layers occurs along the a-axis and in the bc-plane, respectively.

✓

The metal cations Cu⁺ and RE³⁺, in tetrahedral and octahedral coordinations, respectively, are surrounded by tellurium ions with different symmetry operations in the space groups Pnma and Cmcm.

✓

The Eu²⁺ cation has a different coordination environment depending on the compound’s composition. In the compounds EuRECuTe₃ (RE = Y, Nd, Sm–Dy), it is surrounded by seven Te²⁻ anions, forming single-capped trigonal prisms [EuTe₆₊₁]¹²⁻, which are connected by faces and edges, forming chains ${}_{\infty }{}^1\left\{{\left[{\mathrm{Eu}\left(\mathrm{Te}1\right)}_{2/2}{\left(\mathrm{Te}2\right)}_{3/3}{\left(\mathrm{Te}3\right)}_{2/2}\right]}^{4-}\right\}$ along the b-axis. In the compounds EuRECuTe₃ (where RE = Sc, Y, Ho–Lu), Eu²⁺ cations form trigonal prisms [EuTe₆]¹⁰⁻, which are connected by their faces and assemble into one-dimensional chains ${}_{\infty }{}^1\left\{{\left[{\mathrm{Eu}\left(\mathrm{Te}1\right)}_{2/2}{\left(\mathrm{Te}2\right)}_{4/2}\right]}^{2-}\right\}$ along the a-axis.

✓

In the group of EuRECuTe₃ representatives (RE = Sc, Y, Nd, Sm–Lu), the following trends are observed as r_i(RE³⁺) decreases:

✓

The lattice parameters and unit cell volume decrease: a_Pnma(c_Cmcm) by 5.9%, b_Pnma(a_Cmcm) by 3.3%, c_Pnma(b_Cmcm) by 1.5%, and V by 10.5% (Figure 2).

✓

The distance d(RE–Te) decreases by 5.9% (Figure 3).

✓

The degree of distortion of the tetrahedral polyhedra decreases, while that of the octahedral polyhedra increases (Table 1, Figure 5). Tetrahedra and octahedra are stable structural motifs in the EuRECuTe₃ compound series. It is likely that the opposite changes in the degree of distortion of the polyhedra forming the ${}_{\infty }{}^2\left\{{\left[\mathrm{Cu}RE{\mathrm{Te}}_3\right]}^{2-}\right\}$ layer lead to compensation of the overall distortion of the layer and, therefore, the orthorhombic symmetry is preserved throughout the entire series of compounds.

✓

The gradual increase in the symmetry of the structure occurs not only with a decrease in the ionic radius of RE³⁺ (this work, [47,48,49]), but also with an increase in temperature by 30 K [40].

✓

The crystal-chemical compression of the parallel layers ${}_{\infty }{}^2\left\{{\left[\mathrm{Cu}RE{\mathrm{Te}}_3\right]}^{2-}\right\}$ reduces the number of anions coordinating Eu²⁺.

✓

The valence states of the Eu, RE, and Cu ions in the entire EuRECuTe₃ series are close to 2, 3, and 1 (Table S6 in the Supplementary Materials, [40,47,48,49]).

The data obtained for the tellurides complement the information on the isostructural chalcogenides EuRECuS₃ and EuRECuSe₃ and have been plotted on the structural-field map for quaternary copper chalcogenides EuRECuCh₃ (Ch = S [8,11,12,13,14,15,16,36,37], Se [9,10], Te (this work, [40,47,48,49])) and MRECuTe₃ (M = Ba [21,24,26,28], Sr [52], Eu (this work, [40,47,48,49])) (Figure S2 in the Supplementary Materials). Dependencies of the ionic radii of divalent anions r_i(Ch²⁻) = S²⁻, Se²⁻, Te²⁻ and cations r_i(M²⁺) = Ba²⁺, Sr²⁺, Eu²⁺ on the ionic radii of rare-earth metal cations r_i(RE³⁺) = Sc, Y, Nd, Sm–Lu have been constructed. The boundaries of the colored fields correspond to the demarcation lines between different structural types. When moving from S²⁻ to Se²⁻ and further to Te²⁻, an expansion of the anionic sublattice occurs. An increase in the sublattice size by 7% when replacing S²⁻ with Se²⁻ does not affect the position of the boundary between the space groups Pnma and Cmcm, which still runs between the heavy rare-earth elements Ho and Er. However, a further increase in the sublattice by 10.4% when moving from Se²⁻ to Te²⁻ slightly shifts the Pnma → Cmcm transition boundary to the region between Dy, Ho or Y.

Compounds with light rare-earth metals show greater sensitivity to changes in the sublattice size: thus, when transitioning from sulfides to selenides, the change in structural type Ba₂MnS₃ → BaLaCuS₃ occurs at the Pr or Nd and La or Ce boundaries, respectively, while the transition from BaLaCuS₃ to Eu₂CuS₃ occurs at the Nd or Sm and Ce or Pr boundaries. Changes in the cationic sublattice have a more noticeable effect on structural transitions in the series of quaternary tellurides. Even a slight increase in the size of the cationic sublattice by 0.8% when replacing Eu²⁺ with Sr²⁺ results in the transition boundary for the heavy elements shifting from Dy or Ho to Tb or Dy. A more significant expansion of the cationic sublattice by 12.5% when moving from Sr²⁺ to Ba²⁺ causes a sharp change in the space group Pnma → Cmcm already for the light rare-earth metals, with the demarcation line lying between La and Pr.

Thus, an increase in the sizes of the chalcogen and divalent metal ions accelerates the onset of structural transitions, leading to an earlier change in both the space group Pnma → Cmcm and the structural type in the series of quaternary tellurides. The cationic sublattice plays a key role in the structure formation of this class of compounds, making it possible to purposefully control the structural features of the compounds by varying the sizes of the cations and anions.

3.2. Magnetic Properties of EuRECuTe₃

First, the experimental field dependencies of the moments of all samples at 300 K (Figure S3 in the Supplementary Materials) were approximated by paramagnetic Curie law: $m=C{\displaystyle \frac{H}{T}}$. From this assumption Curie constants C_300K and their corresponding effective magnetic moments μ_300K were estimated (

Table 2. Magnetic characteristics for EuRECuTe₃ (RE = Nd, Sm, Tb, Dy (this work) and Gd, Er, Y, Lu [40,47,49]).

	Nd	Sm	Gd [47]	Tb	Dy	Er [49]	Y [40]	Lu [47]
χ300K·104 (m3 kmol−1)	2.81	2.99	6.01	6.72	8.26	7.72	3.03	3.20
Exp. μ300K (μB)	7.32	7.56	10.71	11.33	12.56	12.14	7.60	7.82
Exp. μ50–300K (μB)	7.68	7.88	11.14	11.78	13.24	12.39	7.79	8.04
Calc. μ (μB)	8.72	7.982	11.22	12.550	13.279	12.442	7.937	7.937
Exp. C300K (K m3 kmol−1)	0.084	0.090	0.180	0.202	0.248	0.232	0.091	0.096
Exp. C50–300K (K m3 kmol−1)	0.093	0.098	0.195	0.218	0.275	0.241	0.095	0.102
Calc. C (K m3 kmol−1)	0.1196	0.1101	0.1980	0.2475	0.2771	0.2433	0.0990	0.0990
θp (K)	−7.7	−1.1	−6.1	−5.8	−3.8	−4.0	1.5	5.1
Graph. Tc (K)	–	3.5	8.0	6.0	6.5	3.5	3.0	3.0
Cfit (K m3 kmol−1)	0.094	0.098	0.199	0.220	0.276	0.241	–	–
1/χ0 (kmol m−3)	157	29.2	39.8	31.9	10.5	14.5	–	–
σ (kmol K m−3)	7880	1870	13.5	6.38	1.76	37.0	–	–
θ (K)	–55.7	–28.0	7.76	6.31	6.51	3.09	–	–
Tc (K)	–1.16	3.04	7.93	6.41	6.56	4.24	–	–
arrangement	? *	Fi	Fi	Fi	Fi	Fi	F	F

* there are no magnetic transitions in the measured temperature range.

).

Then, based on the experimental data, the following dependencies were calculated: (1) the inverse susceptibilities versus temperature (an external magnetic field of 40 kA∙m⁻¹ applied), and (2) moments per formula unit versus magnetic field (at 2 K). These plots are pictured in Figure 6 and Figure 7.

These temperature dependencies were assumed to follow the Curie–Weiss law: χ⁻¹ = C⁻¹(T − θ_p). In that approximation Curie constants and corresponding effective magnetic moments were calculated. In Table 2, they are designated as C_50–300K and μ_50–300K. The table also contains the values of the Weiss constants θ_p (paramagnetic Curie temperatures) obtained from these calculations.

Analysis of the measurement results allows us to divide the studied compounds of the entire series of EuRECuTe₃ (RE = Nd (this work), Sm (this work), Gd [47], Tb (this work), Dy (this work), Y [40], Er [49], Lu [47]) tellurides into three groups.

The first group includes compounds with RE = Y [40] and Lu [47]. All of them have the following properties. They contain only one type of magnetic ions: Eu²⁺. Their measured paramagnetic parameters (effective magnetic moment μ and Curie constant C) are in good agreement with the parameters of independent ions (Table 2). Their paramagnetic Curie temperatures θ_p are positive. At low temperatures the thermal dependencies of magnetic susceptibility exhibit signs of a phase transition (in the form of kinks and divergences in the curves for FC and ZFC modes) [40,47]. Table 2 shows the values of critical temperatures Graph T_c, approximately corresponding to these points on the graphs. At considerably high temperatures the thermal dependencies very well obey the Curie-Weiss law. Their magnetization curves at 2 K for have a typical appearance for soft ferromagnets. The saturation magnetization per formula unit is close to the theoretical value for the Eu²⁺ ion (7 μ_B). All of this allows to conclude that these compounds are soft ferromagnets.

The second group includes compounds with RE = Gd [47], Tb (this work), Dy (this work), and Er [49]. They contain two types of magnetic RE³⁺ ions, so they are expected to form two magnetic sublattices. Their measured paramagnetic parameters (effective magnetic moment μ and Curie constant C) are also in good agreement with the parameters of independent ions (Table 2). Their θ_p parameters are negative, indicating that magnetic moments in the paramagnetic state are partially negatively coordinated. The shapes of inverse susceptibility plots in the low-temperature region (Figure 6) are typical of ferrimagnetic compounds. So, these plots were approximated by the Néel hyperbolic formula for two-sublattice ferrimagnets: χ⁻¹ = T/C + χ₀⁻¹ − σ/(T − θ). The values of C denoted as C_fit, χ₀, σ, and θ are given in Table 2. The table also shows the values of the critical temperatures T_c, calculated using the formula T_c = (θ − C/χ₀ + ((θ − C/χ₀)² + 4C(θ/χ₀ + σ))^0.5)/2. The magnetization curves at 2 K (Figure 6) show kinks, indicating different behavior of the magnetic ions’ sublattices of different types in an external magnetic field. Saturation is not achieved even up to fields of 4 MA∙m⁻¹, confirming the conclusion about the ferrimagnetic structure of these compounds.

Finally, the third group includes compounds with RE = Nd (this work) and Sm (this work). Their paramagnetic Curie temperatures are negative (Table 2), like those of the second group, and at sufficiently high temperatures, their magnetic ions are also partially negatively coordinated. However, the graphs of the temperature dependencies of inverse susceptibility for these compounds are almost linear from 300 K to 4 K, similar to ferromagnets. Below 4 K, signs of a phase transition are observed in compounds with Sm, while sample of EuNdCuTe₃ shows no such signs down to 2 K.

Nevertheless, considering that the curvature of the hyperbola decreases as it moves away from the foci, a successful attempt was made to approximate these experimental curves using the above Néel formula. The results of the approximation are shown in the graphs (Figure 6), and the calculated parameters are in Table 2. Notably, the sign of the parameter θ, which determines the position of the vertical asymptote of the hyperbola on the graph χ⁻¹ vs. T, differs from the parameters for the second group’s compounds. A negative θ in Néel theory means that at least one sublattice of the ferrimagnet does not reach saturation at 0 K. In cases where T_c < 0, as for EuNdCuTe₃ sample, both sublattices remain unsaturated, meaning the sample remains paramagnetic down to 0 K.

These conclusions are consistent with the magnetization graphs of the samples as a function of the external magnetic field magnitude (Figure 7). Firstly, they are smooth, resembling the behavior of a single sublattice. Secondly, in the maximum field of 4 MA∙m⁻¹, the magnetization is far from the theoretical total values of 10.27 and 7.71 μ_B for RE = Nd and Sm, respectively. However, for RE = Sm, there are signs of saturation in one sublattice, specifically the Eu²⁺ ion sublattice, near the theoretical value of 7 μB. The EuNdCuTe₃ sample is magnetized weaker. Thus, it should be concluded that the Sm compound has two oppositely oriented sublattices, one of which is saturated and the other is not, while Nd compound remains in an unordered state.

The experimental magnetic characteristics are In good agreement with the calculated ones and correlate with the sulfide and selenide derivatives of EuRECuCh₃ (Ch = S, Se).

A magnetic field map of europium chalcogenides EuRECuCh₃ (Ch = S, Se, Te) was constructed (Figure S4 in the Supplementary Materials), according to which in the range EuGdCuCh₃—EuTmCuCh₃ the compounds are low-temperature ferrimagnets, while representatives of the rest of the series of quaternary chalcogenides exhibit ferromagnetic properties.

3.3. Phonons

The phonon mode frequencies and types derived from the DFT calculations are presented in the Supplementary Materials, specifically in Tables S7–S10. The contribution of each ion to individual phonon modes can be assessed by analyzing the displacement vectors obtained from these DFT calculations (Figure 8). The results of modeling the Raman spectrum of crystals EuRECuTe₃ (RE = Sm, Gd) at Pnma phase compared to experimental one are presented in Figure 9. The spectrum simulation was made in assumption of powder sample in parallel (VV) and crossed (VH) polarizations. The VV spectra shows the presence of at least two intense Raman peaks of A_g type. Calculations indicate that the Ag phonon mode, with an approximate frequency of 60 cm⁻¹, mainly involves copper and europium ions. In the intensive mode with a frequency of about 150 cm⁻¹, tellurium ions are predominantly involved (Figure 8, Table S7, in the “Participating ions” column). The phonon frequencies of crystals EuRECuTe₃ with Pnma structure do not exceed ~200 cm⁻¹. Since the spectrum is confined to low frequencies, all ions participate simultaneously in these modes. This is reflected in Tables S7–S10, under the “Participating ions” column. Europium and copper ions are significantly engaged in modes of frequency with approximately 90 cm⁻¹ and 150 cm⁻¹, respectively. Additionally, rare earth RE³⁺ ions play a prominent role in phonon modes whose frequencies in the range up to 80 cm⁻¹. Tellurium ions contribute significantly in all frequency range (Figure 8). The calculations reveal a phonon gap about 95–110 cm⁻¹. Furthermore, the findings suggest that the majority of vibrational modes involve all or nearly all ions. However, it is possible to identify individual phonon modes in which participate only one or two types of ions.

As an example, Te1 and Te2 ions predominantly contribute to the B_2u (109 cm⁻¹) and the B_1g (114 cm⁻¹) modes. Dy³⁺ and Te²⁻ ions are the main participants in the A_g (154 cm⁻¹) and B_3u (155 cm⁻¹) modes. The most intense IR and Raman modes are illustrated on Figure 10.

The comparison of simulated spectra in Figure 9a–d with experimental ones (Figure 9c,d) demonstrates a fair correlation. Due to spectrometer limit, only part of Raman spectrum above 75 cm⁻¹ was recorded. In order to analyze experimental data, the spectrum was decomposed on set of oscillators using Lorentzian shape fitting. One can find the strong band at c.a. 125 cm⁻¹ accompanied with satellites in low and high frequency wings of the band. This feature is well reproduced in simulated spectra. The band at ~175 cm⁻¹ is damped in experimental spectra, which is probably due to random orientation of the sample, which does not fully correspond to the parallel polarization experimental setup. Comparing spectra for two compounds with RE = Sm, Gd one can find the similarity of the spectra shape—the only difference is band positions, which are slightly shifted towards high frequencies for EuSmCuTe₃ compound. Therefore, the dynamical properties of EuRECuTe₃ crystal series are very similar and obtain only slight influence on variation in rare-earth element.

3.4. Band Structure of EuRECuTe₃

Since hybrid DFT functionals overestimate the band gap value, we used a non-hybrid functional PBE to calculate the band structure. Note, that band structure of range of quaternary chalcogenides was calculated with PBE functional too [38]. We calculated band structure and density of states (Figure 11). Figure 11 does not display 4f states since pseudopotentials “4f in core” were used for rare earth ions. By building the band structure path within the Brillouin zone connects points Γ–X–Z–U–Y–S–T–R–Γ with coordinates (0,0,0), (1/2,0,0), (0,0,1/2), (1/2,0,1/2), (0,1/2,0), (1/2,1/2,0), (0,1/2,1/2), (1/2,1/2,1/2), and (0,0,0), respectively. These are the high-symmetry points of the orthorhombic lattice. The top of the valence band consists of tellurium and copper states. The bottom of the conduction band consists of europium and RE³⁺ ion states (Figure 11).

Band gap values in the “HOMO-LUMO” estimation are presented in

Table 3. Band gap of EuRECuTe₃, eV.

RE	Nd	Sm	Gd	Tb	Dy
Band gap	0.45 (direct)	0.45 (direct)	0.47 (direct)	0.48 (direct)	0.48 (direct)

. The calculations show Γ–Γ direct band gap. The estimated band gap value is approximately 0.5 eV.

The inclusion of f-electrons for the rare-earth elements in the computational scheme makes self-consistent calculations of electronic structure far more difficult. Such spin-unrestricted calculations using the GGA+U (U = 5 eV) method as implemented in the GPAW software package [68] were performed for EuRECuTe₃ (RE = Gd, Tb, Dy) compounds including different magnetic order considerations. The calculated bandstructures for ferrimagnetic spin ordering (spin moments are anti-collinear for magnetic sublattices of different rare-earth elements) are plotted in Figure 12a–c. One can find a clear magnetic ordering due to difference in the bandstructure for states with spin up and spin down states. It is noteworthy that in the conduction band, some states with spin up from a high density sub-band with small dispersion, which normally correspond to highly localized states formed by f- or d- electrons. In order to estimate the nature of these states, the projection density of states was calculated and plotted for EuDyCuTe₃ compound in Figure 12d. The analysis shows that there are strong bands in the range of valence band top, which can be attributed to f-states of the Eu atom. The other strong band in the conduction band bottom is clearly observed in the PDOS of the other rare-earth element—Dy. There are two bands, and both correspond to f-states of Dy atom, where the lowest energy states take part in optical properties and determine the value of the bandgap.

The bandgap values for EuRECuTe₃ (RE = Gd, Tb, Dy) compounds are represented in

Table 4. Bandgap values in GGA+U calculations with f-electrones included in pseudopotential.

	EuGdCuTe3	EuTbCuTe3	EuDyCuTe3
Eg, eV	0.45	0.41	0.53

.

The calculation of total energy of different EuRECuTe₃ for different magnetic orderings was tested, namely the general state ferrimagnetic (FIM-I) with spins being parallel in each sublattice (first sublattice related to spin moments on Eu atoms and second one related to spin moments on RE atoms). The second configuration is ferromagnetic with all spin moments collinear (FM). The third configuration is antiferromagnetic ordering in the Eu sublattice and ferromagnetic for the RE sublattice (AFM-I) and vice versa for fourth configuraion (AFM-II). The difference on energy for abovementioned configuration is given in

Table 5. Different of energy with respect to general ferrimagnetic state in meV.

	EuGdCuTe3	EuTbCuTe3	EuDyCuTe3
FM	13.1	14.7	5.11
AFM-I	8.3	9.4	6.8
AFM-II	12.1	7.38	11.29

.

It is noteworthy that all values in Table 5 are positive, which means that these configurations are less preferable than the ferrimagnetic configuration, which perfectly fits the experimental data.

3.5. Elastic Properties

Calculated elastic constants, as elastic moduli for EuRECuTe₃ crystals, are presented in

Table 6. Calculated properties of EuRECuTe₃ crystals (RE = Nd, Sm, Gd, Tb, Dy). Elastic constants (C_ij), GPa. Elastic moduli: Bulk (B), (G), Young’s (Y), Poisson’s ratio (ν). Universal anisotropy index (A^U).

RE	C11	C12	C13	C22	C23	C33	C44	C55	C66	Calculation Scheme	B	Y	G	ν	Au
	100	37	46	117	48	83	37	14	29	Voigt	62.5	71.5	27.3	0.309	0.80
Nd										Reuss	61.9	62.7	23.6	0.331
										Hill	62.2	67.1	25.4	0.320
	100	39	48	118	50	89	41	8	30	Voigt	64.5	71.5	27.2	0.315	0.59
Sm										Reuss	64.0	51.8	19.0	0.365
										Hill	64.2	61.8	23.1	0.340
	109	39	47	120	52	92	43	8	31	Voigt	66.4	74.6	28.4	0.313	2.26
Gd										Reuss	66.0	53.5	19.6	0.365
										Hill	66.2	64.3	24.0	0.338
	106	40	46	120	51	92	43	8	31	Voigt	65.7	74.5	28.4	0.311	2.25
Tb										Reuss	65.3	53.5	19.6	0.363
										Hill	65.5	64.2	24.0	0.337
	112	40	47	120	51	93	44	8	31	Voigt	66.7	76.0	29.0	0.310	2.13
Dy										Reuss	66.3	55.4	20.4	0.361
										Hill	66.5	65.9	24.7	0.335

. The dependence of Young’s modulus on direction in crystal can be utilized to assess the elastic anisotropy (Figure 13).

The universal anisotropy index A^U [49] (1) have been calculated for the crystals EuRECuTe₃ [69]:

$$A^U=5\left({\displaystyle \frac{G_V}{G_R}}\right)+{\displaystyle \frac{B_V}{B_R}}-6$$

(1)

In term (1), G is the shear modulus, and B is the bulk modulus calculated using either the Reuss (R) or Voigt (V) approximation. The more the index A^U deviates from zero, the higher the degree of anisotropy. The EuRECuTe₃ crystals (RE = Nd, Sm, Gd, Tb, Dy) exhibit notable anisotropy in their elastic properties, as shown in Table 6.

3.6. Layered Structure of EuRECuTe₃

The properties of the single-layer structure were studied using the approach previously reported in paper [40]. The simulations of layered structure were carried out by step-by-step unitcell volume expansion until the structure become clearly composed of layers with a gap between layers. Then, the single layer was extracted, and the symmetry was determined by applying symmetry operations of parent space group. The resulting layered group for all studied compounds is determined as pm2_1b (# 28).

Next, the structural parameters for monolayered samples were obtained using geometry relaxation procedure and exfoliation energy is established using the following equation:

$$E_{exf}=E_{bulk}-E_L$$

where E_bulk and E_L are total reduced energies for bulk and monolayer. The obtained values are represented in

Table 7. Monolayer exfoliation energy for EuRECuTe₃.

RE	Nd	Sm	Gd	Tb	Dy
Eexf, meV	228	233	237	238	236

.

The obtained values are little bit smaller than the one obtained for EuRECuTe₃ [52] but are still too much for mechanical exfoliation; therefore, the synthesis should be made using enhanced techniques like molecular beam epitaxy.

4. Conclusions

Thus, by applying the ampoule synthesis method with the use of a flux, we synthesized orthorhombic single crystals of four new layered tellurides EuRECuTe₃ (RE = Nd, Sm, Tb, Dy) with Pnma symmetry. Based on the analysis of data obtained using a SQUID magnetometer, the EuRECuTe₃ tellurides were classified according to their low-temperature magnetic properties. Compounds with RE = Y and Lu were identified as soft ferromagnets, while those with RE = Gd, Tb, Dy and Er were classified as ferrimagnets, showing different behavior of the Eu²⁺ and RE³⁺ sublattices in an external magnetic field; in addition, the Sm-containing ferrimagnet was distinguished by the saturation of one sublattice (Eu²⁺). The regions of manifestation of ferro- and ferrimagnetic properties in the chalcogenides EuRECuCh₃ (Ch = S, Se, Te) were identified, as well as the ranges of existence of various structural types of quaternary chalcogenides. In addition to the established structural and magnetic regularities, electronic structure calculations showed that the new tellurides EuRECuTe₃ (RE = Nd, Sm, Tb, Dy) are narrow-bandgap semiconductors with a direct band gap of 0.45–0.48 eV. The analysis of the anisotropy of elastic properties revealed a pronounced directional dependence of the Young’s modulus, indicating the potential suitability of these materials for the creation of flexible micro- and nanoelectronic components. The obtained results on exfoliation of individual layers and the calculated energetic parameters confirm the possibility of obtaining stable two-dimensional crystals possessing a unique combination of magnetic and electronic properties. This opens up prospects for further research in the field of two-dimensional magnetic materials, as well as for the development of new heterostructures based on them.