First-Principles Investigation of the Structural, Magnetic, and Electronic Properties of Janus MXene Material CrScCO₂

Abstract

This study employed first-principles density functional theory (DFT) to systematically investigate the influence of oxygen (–O) functional groups on the structural, magnetic, and electronic properties of Janus MXene CrScC. Nine distinct CrScCO₂ configurations with varying oxygen adsorption sites were examined. All configurations exhibited robust ferromagnetic ordering, with total magnetic moments ranging from 1 to 3 μ_B, predominantly contributed by Cr atoms. Notably, the majority of the configurations exhibited half-metallic behavior, characterized by fully spin-polarized conduction channels and half-metallic gaps spanning 0.23–1.54 eV, with one configuration approaching a spin-gapless semiconductor characterized by a minimal bandgap (<0.1 eV). The ground-state configuration demonstrated strong performance, featuring a 100% spin polarization ratio and a wide half-metallic gap of 0.44 eV, indicating significant potential for spintronic applications. Phonon spectrum calculations confirmed the dynamic stability of the half-metallic ground-state structure, while binding energy analysis highlighted the enhanced stability of the oxygen-functionalized system compared to pristine CrScC. These results demonstrate that –O functional groups play a key role in modulating the magnetism and electronic properties of CrScC, offering versatility for various spintronic device applications.

1. Introduction

Since the first discovery of the two-dimensional MXene material Ti₃C₂ by Gogotsi and Barsoum in 2011, research on MXene materials has flourished, leading to the synthesis of numerous MXenes with diverse compositions and structures [1]. These materials, characterized by their unique atomic arrangements and exceptional properties, have found extensive applications in fields such as electrochemistry, energy storage, catalysis, and environmental remediation [2,3,4]. Among these applications, spintronic devices—which rely on precise control of spin-polarized electronic states—demand materials with tunable magnetism and high spin polarization. MXenes, especially those with asymmetric structures, offer a promising platform for such technologies due to their versatile surface chemistry and emergent magnetic properties. The exploration of MXenes with varied structures and the prediction of their properties has become a central focus of research in two-dimensional (2D) materials, driven by their potential to revolutionize a broad range of technologies [5]. MXenes are typically composed of layers of transition metal carbides, nitrides, or carbonitrides, with a general formula of M_n+1X_nT_x [5], where M represents transition metals such as Ti, Zr, V, Mo, and Cr, X is C or N, and T denotes surface functional groups like –OH, –O, –F, and –Cl. These surface functional groups play a crucial role in significantly influencing the mechanical, electrical, stability, and magnetic properties of MXenes [6,7].

In recent years, the synthesis of bi-transition-metal MXenes, such as Mo₂TiC₂T_x and Ti₃C₂T_x, has further expanded the range of MXenes, with these materials exhibiting intriguing properties [8]. However, despite their structural similarities, these MXenes often show markedly different electrochemical and magnetic behaviors, highlighting the need for deeper understanding of how their composition and surface modifications influence their performance [9]. In particular, the magnetic and electronic properties of Cr₂M′C₂T₂ MXenes can be effectively tuned by varying the transition metal element M′ and the surface functional groups T [10], which highlights the complex interplay between material composition, surface chemistry, and intrinsic properties, remaining an important area of investigation. For instance, Cr₂CO₂ exhibits ferromagnetic semiconducting behavior, while Cr₂C functionalized with –F groups shows half-metallic properties [11,12]. Such tunability positions chromium-based MXenes as potential components in spin valves, magnetic memory devices, and spin-polarized electrodes [13].

The study of MXene magnetism is particularly promising for advancing nanoscale electronics and spintronics. MXenes with magnetic properties are at the forefront of new developments in 2D magnetic, magnetoelectric, and magneto-optical applications. While numerous MXene materials have been theoretically predicted, most are non-magnetic or exhibit low spin polarization. In contrast, chromium-based MXenes have shown exceptional magnetoelectric properties, making them particularly interesting for such applications [13,14]. For example, Cr₂N is an antiferromagnetic metal, and its magnetic properties remain unchanged when functionalized with –F or –OH groups. However, modification with –O leads to a transition to ferromagnetism [11]. Similarly, Cr₂C displays half-metallic ferromagnetism, which can be altered by surface modifications such as –F, –H, –OH, or –Cl [12], and Cr₂CO₂ behaves as a ferromagnetic semiconductor [15]. These findings suggest that careful surface engineering can significantly influence the magnetic characteristics of MXenes, opening new avenues for material design.

The symmetry of 2D materials is also a critical factor affecting their properties. Symmetry breaking, induced by structural modifications or surface functionalization, can lead to phase transitions and a modification of magnetic properties, as well as enhancement of other material characteristics [16,17]. For instance, the asymmetric Ta₂CS₂ MXene exhibits dramatically higher thermal conductivity compared to its symmetric counterpart, underscoring the role of symmetry in determining material behavior [18]. Janus MXenes, which possess asymmetric surface properties, represent a class of materials where symmetry breaking introduces novel electromagnetic and magnetic properties. Studies on Janus MXenes, such as M₂XO_xF_2−x, have shown that local structural and chemical disorders can induce magnetic ordering in otherwise non-magnetic or weakly magnetic systems [19]. Moreover, Janus functionalization can enhance magnetic anisotropy, providing a new pathway for the tuning of magnetic properties via surface modification. However, systematic studies on Janus MXenes combining chromium with lighter transition metals (e.g., Sc) are scarce, despite the potential for such systems to exhibit enhanced spin–orbit coupling and unconventional magnetic configurations [10,13].

The magnetic properties of asymmetrically structured bimetallic MXenes have also been actively investigated. Research has demonstrated that Janus chromium-based bimetallic carbides, such as CrVC and CrTiC, exhibit unique electronic and magnetic properties. These materials show half-metallic or metallic behavior that can be easily switched to half-metallic states under external influence, offering promising prospects for spintronic applications [13]. Nevertheless, the Cr–Sc system functionalized with –O groups remains underexplored, despite scandium’s ability to modulate electronic band structures through its distinct atomic size and electronegativity, which may synergize with Cr’s magnetic properties to achieve novel functionalities.

This work systematically examined how asymmetric surface functionalization modulates magnetic anisotropy and electronic states in Janus-structured chromium-based bimetallic MXenes, with CrScCO₂ as a representative system. Using first-principles density functional theory (DFT) calculations, we examined the geometric structure, magnetic, and electronic properties of Janus CrScCO₂ at the atomic scale. The results show that all the configurations exhibited robust ferromagnetic ordering and that the majority of the configurations exhibited half-metallic behavior. The ground-state configuration had a 100% spin polarization ratio and a wide half-metallic gap, indicating significant potential for spintronic applications.

2. Computational Details

In this study, spin polarization calculations were performed using first principles based on DFT, and all the calculations were implemented in CASTEP software [9,10]. The Perdew–Burke–Ernzerhof (PBE) functional, widely used for its balance between computational efficiency and accuracy in systems involving transition metals and their compounds, within the generalized gradient approximation (GGA), was utilized to describe exchange-correlation energy [14]. Electronic–ion interactions were treated using the ultrasoft pseudopotentials method [9], with a cutoff energy of 400 eV. Based on previous research, Hubbard U values of 4 eV were introduced for the d-electrons of transition metal atoms Cr and Sc to ensure accurate electronic structure [13]. The U parameter helped correct for the self-interaction error inherent in the standard DFT approach, particularly for transition metals with localized d-electrons, and it has been shown to improve the description of magnetic and electronic properties in such systems [20,21]. The energy convergence criterion for ionic steps was set to 1 × 10⁻⁵ eV per atom, while for electronic structure the self-consistent field was set to 1 × 10⁻⁶ eV. The convergence criterion for forces was 0.02 eV Å⁻¹. Brillouin zone sampling was performed using the Monkhorst–Pack method, with a k-point density of 2π × 0.025 Å⁻¹ [22]. Both the cutoff energy and k-point sampling were converged to ensure atomic energy convergence within 0.002 eV. To more accurately characterize the weak interactions in the system, the van der Waals (vdW) interactions were described using the Grimme method [11,23]. To simulate 2D planes within a three-dimensional periodic system, a vacuum layer of approximately 20 Å was added along the z-axis to prevent interaction between periodic images of the 2D material and ensure that the simulation accurately represented the isolated monolayer behavior of MXenes. To perform the calculations for isolated atoms, we placed them in a 20 Å × 20 Å × 20 Å three-dimensional box to ensure that the atoms were sufficiently separated to avoid interactions between periodic images.

The phonon spectrum was calculated by the phonopy program using a 3 × 3 × 1 supercell [15]. For the 2D MXene material CrScC, the formulas for calculating the binding energy E_b and formation energy E_f are as follows [19]:

$$E_{\mathrm{b}}={\displaystyle \frac{1}{3}}{E}_{\mathrm{atom}}\left(\mathrm{Cr}\right)+{\displaystyle \frac{1}{3}}{E}_{\mathrm{atom}}\left(\mathrm{Sc}\right)+{\displaystyle \frac{1}{3}}{E}_{\mathrm{atom}}\left(\mathrm{C}\right)-{\displaystyle \frac{1}{3}}E\left(\mathrm{CrScC}\right)$$

(1)

where E_atom(Cr) represents the energy of a single Cr atom, E_atom(Sc) denotes the energy of a single Sc atom, E_atom(C) is the energy of a single C atom, and E(CrScC) represents the total energy of CrScC. A positive value indicates that the material can exist stably;

$$E_{\mathrm{f}}={\displaystyle \frac{1}{3}}E\left(\mathrm{Cr}\right)+{\displaystyle \frac{1}{6}}E\left(\mathrm{Sc}\right)+{\displaystyle \frac{1}{12}}E\left(\mathrm{C}\right)-{\displaystyle \frac{1}{3}}E\left(\mathrm{CrScC}\right)$$

(2)

where $\mathit{E}$(Cr) represents the energy of a body-centered cubic Cr primitive cell (containing one atom), $\mathit{E}$(Sc) represents the energy of a hexagonal-close-packed Sc primitive cell (containing two atoms), $\mathit{E}$(C) is the energy of a graphite primitive cell (containing four atoms), and $\mathit{E}$(CrScC) represents the total energy of CrScC. A positive value indicates an exothermic reaction when the material is synthesized from simple substances, while a negative value indicates an endothermic reaction. By incorporating the relevant energy of O into the above formulas, the binding energy and formation energy of CrScCO₂ can be obtained:

$$E_{\mathrm{b}}={\displaystyle \frac{1}{5}}{E}_{\mathrm{atom}}\left(\mathrm{Cr}\right)+{\displaystyle \frac{1}{5}}{E}_{\mathrm{atom}}\left(\mathrm{Sc}\right)+{\displaystyle \frac{1}{5}}{E}_{\mathrm{atom}}\left(\mathrm{C}\right)+{\displaystyle \frac{2}{5}}{E}_{\mathrm{atom}}\left(\mathrm{O}\right)-{\displaystyle \frac{1}{5}}E\left({\mathrm{CrScCO}}_2\right)$$

(3)

where E_atom(O₂) represents the energy of a single O atom and E(CrScCO₂) represents the total energy of CrScCO₂;

$$E_{\mathrm{f}}={\displaystyle \frac{1}{5}}E\left(\mathrm{Cr}\right)+{\displaystyle \frac{1}{10}}E\left(\mathrm{Sc}\right)+{\displaystyle \frac{1}{20}}E\left(\mathrm{C}\right)+{\displaystyle \frac{1}{5}}E\left({\mathrm{O}}_2\right)-{\displaystyle \frac{1}{5}}E\left({\mathrm{CrScCO}}_2\right)$$

(4)

where E(O₂) is the energy of an oxygen molecule.

The spin polarization ratio at the Fermi level, denoted as P, can be calculated using the following formula:

$$P={\displaystyle \frac{\left|N_{\uparrow }-N_{\downarrow }\right|}{N_{\uparrow }+N_{\downarrow }}}\times 100\%$$

(5)

where $N_{\uparrow }$ and $N_{\downarrow }$ represent the DOS at the Fermi level for spin-up and spin-down states, respectively.

3. Results and Discussion

3.1. The Geometry and Stability

The 2D MXene material Cr₂C exhibits P-3m1 (No.164) symmetry, where the C atomic layer is located between two layers of positively charged Cr atoms, with the C atom at the center of a tetrahedron formed by six Cr atoms, as depicted in Figure 1a. It can be selectively etched from a Cr₂AlC crystal by removing Al atoms [24]. Our geometric optimization results reveal that Cr₂C possesses lattice constants of a = b = 3.27 Å, a thickness of l = 2.17 Å, and the C–Cr bond length of d_C–Cr = 2.18 Å, as shown in

Table 1. Lattice parameters a, atomic distances d, and interlayer spacings l for Cr₂C and CrScC. Units are Å.

		a	dC–Cr	dC–Sc	l
Cr2C	Current work	3.27	2.18	–	2.17
	Ref. [13]	3.21	2.13	–	2.11
	Ref. [12]	3.13	2.10	–	2.12
	Ref. [25]	2.81	2.09	–	1.93
CrScC	Current work	3.36	2.21	2.32	2.33
	Ref. [13]	3.29	2.09	2.39	2.34

. These values closely align with the DFT+U (U = 4 eV) results obtained by Akgenc et al. [13], whereas they are slightly larger than the DFT results reported by Wu et al. (2.81 Å, 2.09 Å, and 1.93 Å) [25] and Si et al. (3.14 Å, 2.10 Å, and 2.12 Å) [12]. This suggests that parameters such as +U have a significant impact on lattice constants [26].

To investigate the magnetic ground state, the four most possible magnetic coupling configurations, i.e., ferromagnetic (FM) and three antiferromagnetic (AFM) ones (Néel, Stripy, and Zigzag), were considered [27], as shown in Figure 2. Our DFT calculation shows that the FM state had the lowest energy, consistent with the findings reported for many other Cr-based MXenes [28,29]. The magnetic moment of Cr₂C was determined to be 8.00 μ_B, primarily contributed by Cr atoms, consistent with the findings of Si et al. [12]. The calculated density of states (DOS) revealed that the spin-up states of Cr₂C crossed the Fermi level, while the spin-down states exhibited a gap of approximately 2.03 eV at the Fermi level, indicating half-metallic behavior. This spin-down gap value is in good agreement with the results reported by Yu et al. [30] (approximately 2.1 eV) using the PBE+U (U = 3 eV) method. In contrast, it is significantly smaller than the values obtained by Si et al. [12] (approximately 3.6 eV) using the Heyd–Scuseria–Ernzerhof (HSE) screened Coulombic hybrid density functional method, due to the well-known underestimation of bandgaps by PBE-GGA [31]. The half-metallic gap, defined as the energy difference between the Fermi level and the highest occupied spin-down level, was calculated to be 1.39 eV, which is slightly smaller than the value of 1.88 eV reported by Yu et al. [30] and significantly smaller than the value of 2.85 eV reported by Si et al. [12]. This discrepancy may be attributed to differences in the U value or the choice of functional [32]. However, the conclusion here is consistent with previous studies, which identified Cr₂C as a half-metal with a large half-metallic gap.

Replacing one layer of Cr atoms with Sc atoms in the Cr₂C structure yielded the 2D MXene material CrScC, as shown in Figure 1b, with symmetry P3m1 (No.156). The lattice constants of CrScC were a = b = 3.36 Å, l = 2.33 Å, d_C–Cr = 2.21 Å, d_C–Sc = 2.32 Å, as summarized in Table 1, which are close to the results obtained by Akgenc et al. [13]. The incorporation of Sc led to a downward shift of the spin-down band gap, ranging from −1.3 eV to −0.4 eV, disrupting the half-metallic property of the pristine Cr₂C. Both the spin-up and spin-down levels crossed the Fermi level, exhibiting metallic behavior, with a spin polarization ratio of approximately 34%.

To verify the dynamic stability of CrScC, we employed the finite displacement method to compute the phonon spectrum of the 2D MXene material CrScC. A 3 × 3 × 1 supercell with atomic displacements of 0.015 Å was used. The phonon spectrum and the partial density of phonon states (PDPS) are depicted in Figure 3. It can be observed that the three atoms in the unit cell generated a total of nine phonon branches, including three acoustic branches and six optical branches, with a gap of 0.50 THz between the acoustic and optical branches. The main vibration frequencies of the C atoms in the the PDPS were higher than those of the Sc and Cr atoms, consistent with the frequency formula $\omega =\sqrt{k/m}$ in the harmonic oscillator model, where frequencies increase with decreasing atomic mass. The PDPS for the Sc and Cr atoms were very similar, which can be attributed to the similar atomic masses and environments of these two types of atoms. This suggests that the vibrational behavior of Sc and Cr atoms is nearly identical in the CrScC structure, which is important for maintaining overall lattice stability. Moreover, no imaginary frequencies were found throughout the Brillouin zone, indicating the absence of soft modes that could lead to lattice instability or phonon-driven phase transitions. This confirms that the CrScC material remained stable under small atomic displacements, supporting its potential for practical applications in various fields. Our phonon spectrum results are consistent with those obtained by Akgenc et al. [13] using a 5 × 5 × 1 supercell, indicating that our 3 × 3 × 1 supercell is sufficient to produce accurate phonon spectra and further affirming the reliability of our computational results.

To further validate the stability of the 2D MXene material CrScC, we also calculated its binding energy and formation energy according to Equations (1) and (2), respectively. The binding energy is 4.02 eV, a positive value indicating that CrScC is stable, while the formation energy is −0.82 eV, a negative value indicating that the synthesis of CrScC is an endothermic reaction.

We introduced –O surface functional groups to modify CrScC based on its optimized structure. Considering three adsorption positions on two surfaces—above the first layer of atoms (denoted as 1), above the second layer of atoms (denoted as 2), and above the third layer of atoms (denoted as 3)—we designed nine Janus asymmetric CrScCO₂ configuration models. After geometry optimization, the corresponding stable configurations were obtained, as illustrated in Figure 4.

Figure 5 illustrates the lattice constants, bond lengths, and thickness (the distance between the Cr atomic layer and Sc atomic layer) of the nine optimized Janus CrScCO₂ configurations. As can be seen in Figure 5, the lattice constant of CrScCO₂-11 was closest to that of CrScC, since all O atoms are adsorbed on the top sites of the surface atoms, and the O atoms have less influence on the interatomic interactions of CrScC. Other configurations had at least one layer of O atoms adsorbed on the hollow sites composed of Cr or Sc atoms, and one O atom bonded to three Cr or three Sc atoms, resulting in a large effect on the original interatomic interactions and a large change in the lattice constant. When the lattice constant increased the thickness decreased, and, conversely, when the lattice constant decreased the thickness increased, indicating that the increase in the lattice constant may have been due to the reduction in interlayer spacing.

One layer of O atoms located at the top sites of the Cr atoms in CrScCO₂-11, CrScCO₂-21, and d_O–Cr was relatively small. The differences in d_O–Cr were not significant in other configurations, because the O atoms were located at the hollow sites composed of Cr atoms, forming bonds with three Cr atoms, and a similar trend was observed for d_O–Sc. The variations in d_C–Cr were influenced by O atoms and followed a pattern similar to d_O–Cr, whereas the C atomic layer was located in the middle layer, resulting in smaller variations. The influence of O atoms on d_O–Sc and, subsequently, on d_C–Sc followed a pattern similar to the influence of O atoms on d_O–Cr and d_C–Cr. The variations in d_C–Cr and d_C–Sc led to changes in thickness, which, in turn, affected the lattice constants.

To investigate the relative stability of the CrScCO₂ configurations, we calculated their energy ΔE (relative to CrScCO₂-32), binding energy E_b, and formation energy E_f, as shown in

Table 2. The energy ΔE (relative to that of CrScCO₂-32), binding energy E_b, formation energy E_f, and magnetic moment M of the CrScCO₂ configurations. The energy unit is eV, and the magnetic moment unit is μ_B.

	ΔE	Eb	Ef	Mtotal	MCr	MSc
CrScCO2-11	5.26	4.76	−0.03	1.00	2.62	0.14
CrScCO2-12	5.32	4.75	−0.04	1.00	3.58	0.03
CrScCO2-13	4.53	4.91	0.11	1.00	3.43	0.04
CrScCO2-21	1.50	5.51	0.72	1.00	2.19	0.00
CrScCO2-22	0.31	5.75	0.96	3.00	3.88	−0.10
CrScCO2-23	1.30	5.55	0.76	1.00	3.25	−0.17
CrScCO2-31	1.02	5.61	0.81	1.00	2.23	−0.06
CrScCO2-32	0.00	5.81	1.02	3.00	4.03	−0.13
CrScCO2-33	0.84	5.64	0.85	1.20	3.30	−0.12

. Among all the configurations, CrScCO₂-32 had the lowest energy, indicating that it is the most stable. The binding energies of all the CrScCO₂ configurations were positive, indicating their stability, and they were higher than those of Cr₂C (3.62 eV) and CrScC (4.02 eV), suggesting that Sc substitution enhances stability. Except for CrScCO₂-11 and CrScCO₂-12, which had negative formation energies, the formation energies of the other configurations were positive, implying exothermic reactions during experimental synthesis. Further analysis of the other configurations can be found in the Supplementary Information. Upon substituting Cr with Sc, the most stable configuration for CrScCO₂ became CrScCO₂-32. The position of the O atom on the Cr side remained unchanged, but on the Sc side it shifted from site 2 to site 3. It is worth noting that Cr₂CO₂-22 and Cr₂NO₂-33 are the most stable configurations [33,34]. This demonstrates that functional groups and element substitution have an impact on the structure and stability of MXene materials.

To further validate the stability of CrScCO₂-32, we also computed its phonon spectrum and PDPS, as shown in Figure 6. A total of 15 phonon spectral lines were generated from the five atoms, comprising three acoustic branches and 12 optical branches. The presence of surface O atoms altered the local environment of the Cr and Sc atoms, leading to significant differences in the PDPS for the Cr and Sc atoms. The phonon states associated with the low-frequency portion of the O atoms and the movement of the Cr and Sc atoms towards lower frequencies resulted in the disappearance of the band gap between the acoustic and optical branches in CrScC. The disappearance of the band gap between the acoustic and optical branches may have been related to the vibration modes of the oxygen atoms in the low-frequency region. The low-frequency vibrational modes of the O atoms interacted with the vibrations of the Cr and Sc atoms, leading to changes in the overall vibrational modes of the material, which affected the phonon spectrum gap. Despite this, no imaginary frequencies were observed across the entire Brillouin zone, indicating that CrScCO₂-32 is dynamically stable.

It is also noteworthy that the PDPS of the Cr and Sc atoms exhibited significant differences, suggesting distinct vibrational characteristics for these two elements within the configuration. This could be attributed to their atomic masses and chemical environments, highlighting the important role of the different components of the material in its dynamic stability. Additionally, the vibrational modes of the O atoms made a notable contribution to the overall stability of the material, implying that surface modifications with oxygen are critical for regulating the dynamic stability of MXene materials.

3.2. Magnetic and Electronic Structure

To investigate the influence of –O surface functional groups on the magnetism of CrScC, we computed the total magnetic moment and atomic magnetic moments in CrScCO₂, as shown in Table 2. The calculated results indicate that the FM state was energetically favored for all configurations of CrScCO₂, further supporting the stable ferromagnetic ordering in these materials. Specifically, CrScCO₂-32, the most stable configuration, exhibited a total magnetic moment of 3 μ_B, significantly larger than the other configurations, where the magnetic moments were around 1 μ_B.

The larger magnetic moment in CrScCO₂-32 suggests that the interaction between Cr atoms and the –O functional group plays a crucial role in stabilizing the FM phase, likely by enhancing spin polarization and spin alignment through superexchange interactions. This finding is consistent with previous studies that have shown that surface functionalization in MXenes can modulate their electronic structure and magnetic properties [35].

In terms of atomic contributions, the magnetic moments in CrScCO₂-32 were primarily contributed by the Cr atoms, with Sc atoms showing much weaker magnetic moments. This suggests that Cr atoms are the key elements driving the magnetic properties in CrScCO₂, while Sc atoms serve primarily to stabilize the configuration and contribute less to the magnetic interactions. The negatively charged C and O atoms, particularly the –O functional groups, played a critical role in modulating the electronic structure of the Cr and Sc atoms. These surface groups interacted with the metal atoms through superexchange interactions, facilitating the alignment of spins and the formation of the ferromagnetic phase.

Further analysis of the DOS of CrScCO₂-32, shown in Figure 7h, reveals that only the spin-up states crossed the Fermi level, indicating half-metallic behavior. The spin-polarization ratio of CrScCO₂-32 at the Fermi level was 100%, and it had a relatively wide half-metallic gap of 0.44 eV, suggesting its potential application in spin transport devices. The spin-down gap of CrScCO₂-32 was 2.38 eV, which was relatively large. This is consistent with our previous work on Cr2NO₂ [36], where we reported similar conclusions, demonstrating that Cr-based MXenes are promising materials for applications requiring spin-polarized currents.

It is worth noting that the DOS for CrScCO₂-22 (Figure 7e) shows that spin-up states near the Fermi level exhibit a small gap of 0.085 eV, indicating spin-gapless semiconductor behavior. However, applying strain or pressure could potentially reduce the gap to zero, transforming the material into a spin-gapless semiconductor [37]. The spin-down states showed a gap of approximately 1.83 eV, indicating that CrScCO₂-22 exhibits half-metallic behavior for spin-up states, with a significant gap for the spin-down states. This behavior suggests that CrScCO₂-22 has potential for applications in energy-storage devices.

4. Conclusions

This study employed first-principles calculations to investigate the influence of –O functional groups on the properties of Janus MXene CrScC. Nine CrScCO₂ configurations with different oxygen adsorption sites were examined, all showing strong ferromagnetic ordering with total magnetic moments ranging from 1 to 3 μ_B, mainly contributed by Cr atoms. Most of the configurations were half-metallic with half-metallic gaps from 0.23 to 1.54 eV, while one exhibited a near-gapless semiconductor behavior. The ground-state configuration had a 100% spin polarization ratio and a 0.44 eV half-metallic gap. Phonon spectrum and binding energy analyses confirmed the dynamic stability of the ground-state structure and the enhanced stability of the oxygen-functionalized system, respectively. This indicates that –O functional groups are crucial for modulating the properties of CrScC, offering diverse possibilities for spintronic device applications.