Liyenda
Gogoi
and
Pritam
Deb
*
Advanced Functional Materials Laboratory, Department of Physics, Tezpur University (Central University), Tezpur-784028, India. E-mail: pdeb@tezu.ernet.in
First published on 24th November 2025
Interfacial effects have emerged as a promising tool in engineering localized and global magnetic properties of van der Waals heterostructures. Understanding the underlying mechanism of such interfacial effects is crucial for precise control over the interface induced properties and phenomena. Herein, this paper proposes a hypothesis on the deterministic role of atomic sub-orbitals of interfacial atoms in interfacial spin hybridization, which controls the magnetic proximity effect between a magnetic conductor and a non-magnetic material with a band gap. This work demonstrates that the mere presence of electronic bands of adjacent materials in the same energy window in a heterostructure does not ensure interfacial hybridization. Instead, atomic sub-orbitals of interfacial atoms – particularly the pz orbital – are the principal hybridizing agents. We propose that the asymmetric contribution of pz-up and pz-down orbitals to the Fermi level of magnetic conductors is the principal parameter that governs induced magnetism via hybridization proximity in non-magnets.
Janus materials, a unique class of 2D materials, with asymmetric compositional elements on each side,21–34 present an ideal platform for such interfacial studies, offering the opportunity to explore different interfaces while maintaining consistent electronic and magnetic properties in the adjacent materials. These materials facilitate the formation of stacking-dependent heterostructures. Since all other parameters are similar in such heterostructures with different interfaces, exploration of interfacial magnetic effects, such as spin splitting in these types of heterostructures, paves the way for detailed understanding of the effects of interfacial atoms on interlayer magnetic coupling in vdW heterostructures. CrSTe is one such material that has different compositional elements on the two sides, which can be synthesized following the procedures for the synthesis of Janus monolayers.21,22,32,33,35,36 Moreover, despite having a broken mirror symmetry, CrSTe shows very weak Dzyaloshinki–Moriya interaction and has long range ferromagnetic order with perpendicular magnetic anisotropy.37–39 These properties make the material suitable for studying the magnetic proximity effects. For exclusive understanding of the interfacial effect on non-magnetic materials with a band gap, a material with a single atomic layer is a suitable candidate. This is because in such single atomic layer materials, that single layer, which is supposed to be the interfacial layer, controls the global properties of the system. Therefore, any interfacial change is reflected in the global change of properties in the system. Keeping this advantage of single layered materials in view, we consider a SnC monolayer to design a heterostructure with CrSTe due to the minimal lattice mismatch of 1.1% between SnC (lattice constant = 3.49 Å)40 and CrSTe (lattice constant = 3.45 Å)37 and the high band gap of SnC.40
In this article, we report the deterministic role of interfacial atomic orbitals in interfacial magnetic coupling. We demonstrate that spin-dependent interfacial atomic orbital hybridization is controlled by the pz interfacial orbitals and it induces reverse spin splitting in the non-magnet. Our findings reveal that spin-dependent charge transfer between the systems as a consequence of selective hybridization significantly influences their electronic and magnetic properties. Our results show that all the atomic sub-orbitals do not contribute equally to interfacial hybridization. We also discuss the influence of the interface, interfacial atoms, and their orbitals on this hybridization process. Based on the observations, we propose that the asymmetric presence of pz orbitals of interfacial atoms at the Fermi level is essential for inducing magnetism in a non-magnetic system. This proposed orbital selective hybridization explains the cause of the presence or absence of proximity induced magnetism in vdW heterostructures. Our proposed mechanism provides new insights into the prevailing electronic band structure-based understanding of the hybridization-induced magnetic proximity effect.
| Eformation = Etotalheterostructure − EtotalCrSTe − EtotalSnC | (1) |
Moreover, the binding energies of the heterostructures are evaluated using eqn 2:
51,52
| Ebinding = Etotalheterostructure − EtotalCrSTe+SnC | (2) |
In the two heterostructures, the proximity of magnetic CrSTe to non-magnetic SnC suggests a potential magnetic proximity effect. Our initial investigations revealed a strong induced magnetic moment (−0.1225μB) in the C atom of the SnC layer of the CrTeS/SnC heterostructure, which is opposite to the magnetic orientation of CrSTe. This induced magnetic moment has a similar value to earlier reported values of proximity induced magnetic moment in heterostructures and within the experimentally detectable range.53–57 Moreover, since this induced magnetism is subjected to a substrate ferromagnet CrSTe, whose Curie temperature in the heterostructure is estimated to be 285 K (SI Fig. S2), the induced magnetic state will be operable at high temperatures under the influence of the CrSTe's magnetic effect. On the other hand, no magnetism was induced in the SnC layer of the CrSTe/SnC heterostructure. This asymmetric finding is particularly intriguing, as one would expect a similar, albeit not quantitatively identical, magnetic effect of CrSTe on SnC in both heterostructures, due to the similar magnetic environment provided by CrSTe. However, these results demonstrate a completely asymmetric magnetic effect of CrSTe on SnC, driven by variations in the interface and interlayer separation.
To investigate the role of interlayer separation on the induced magnetism, we analyzed two additional heterostructures with adjusted interlayer separations with clamped ion approximation. Specifically, we set the interlayer separation of CrTeS/SnC as equal to that of the optimized CrSTe/SnC and vice versa, as shown in the SI (Fig. S3). While the induced magnetism was slightly reduced in the modified CrTeS/SnC, no magnetism was induced in SnC in the modified CrSTe/SnC. This indicates that interlayer separation is not the primary factor behind the asymmetric magnetic effect. Instead, the asymmetry must stem from an alternative interfacial mechanism. Given the correlation between magnetic and electronic properties, we next examined the electronic properties of the two heterostructures to understand the asymmetric magnetic effect.
Fig. 2 shows the spin-polarized band structures of the two heterostructures compared to the monolayer CrSTe and SnC. CrSTe exhibits spin polarization (Fig. 2(a)), while SnC does not (Fig. 2(b)). In Fig. 2(c) and (d), both heterostructures have bands crossing the Fermi level near the K-high-symmetry point, a feature absent in the pristine monolayers. Notably, the band structures differ significantly between the two heterostructures. In CrSTe/SnC, bands of both spins cross the Fermi level at the K-high-symmetry point without spin splitting, whereas in CrTeS/SnC, bands of only one spin cross the Fermi level, resulting in a strong spin splitting of 447 meV between the majority and minority spin channels at the K-high-symmetry point. This spin splitting between spin up and spin down bands is shown in the SI, Fig. S4. These observations are particularly intriguing because the presence or absence of spin splitting at the K-high-symmetry point correlates with the observed induced magnetism in the SnC layer. This spin splitting at the K-high-symmetry point correlates with induced magnetism in the SnC layer, while the absence of splitting corresponds to an absence of induced magnetism. This suggests that electronic states at the K-high-symmetry point are associated with SnC in the heterostructure, and the interfacial electronic coupling of spin up and spin down bands is asymmetric in CrTeS/SnC. To gain further insights into this asymmetric behavior, we analyzed the projected atomic band structures of the two heterostructures. The projected atomic band structures as shown in Fig. 3(a–d) confirm that the new electronic states above the Fermi level at the K-high-symmetry point are primarily contributed by C-p orbitals. Comparison of the band structures between the heterostructures and the pristine monolayers reveals that the valence band of SnC shifts toward the Fermi level as a result of heterostructure formation, allowing these shifted bands to participate in hybridization and cause the spin splitting of 447 meV in the SnC layer. However, in CrTeS/SnC, only the spin-up electrons from C strongly hybridize with CrSTe as shown in Fig. 3(a), while spin-down hybridization is very weak as shown in Fig. 3(b), as the spin down bands contributed by the SnC in the heterostructure retain the exclusive signature of the SnC bands shown in Fig. 2(b). This result is again very significant because, according to the hybridization proximity theory,20 when both spin-up and spin-down bands of CrSTe are present at the Fermi level, both spin channels of SnC should participate in hybridization with CrSTe. In CrSTe/SnC, both spin channels hybridize weakly, as indicated by the retained SnC band features shown in Fig. 3(c) and (d). These inferences lead to the conclusion that electrons with opposite spins hybridize differently in the CrTeS/SnC heterostructure and hybridization strength depends on the interface. This asymmetric hybridization of spin up and spin down electrons at the interface induces a half-metallic character in the SnC layer in the CrTeS/SnC heterostructure. The PDOS for SnC exhibiting a half-metallic character in CrTeS/SnC is shown in the SI (Fig. S5). SnC in the CrTeS/SnC system has a band gap of zero for the spin-up channel, whereas it has a band gap of 0.73 eV for spin-down channel, which demonstrates the half-metallic characteristics of SnC in the magnetic heterostructure.
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| Fig. 2 Electronic band structures of (a) CrSTe monolayer, (b) SnC monolayer, (c) CrTeS/SnC heterostructure and (d) CrSTe/SnC heterostructure. | ||
To understand the strong spin-dependent hybridization of C atoms with CrSTe in specific interfaces, we examined the projected orbital density of states (PDOS) for pristine CrSTe and the orbital-resolved atomic band structure of CrSTe and SnC. The orbital resolved projected band structures for the surface atoms of pristine CrSTe and SnC are shown in the SI, Fig. S6 and S7. The orbital-resolved PDOS of interfacial atoms shown in Fig. 4(a and b) reveals that the pz orbitals of S significantly contribute to the spin-up bands at the Fermi level, while the pz orbitals of Te contribute minimally and neither of the two pz orbitals contributes to the spin-down band at the Fermi level. These variations of pz orbital contribution align with the observed strength of hybridization in the S-side and Te-side interfaces. Additionally, the valence band maximum in SnC is dominated by C-pz orbitals, allowing pz-up hybridization between C and S at the S-side interface. However, negligible pz-up orbital presence in Te leads to weak hybridization at the Te-side interface. The absence of pz-down orbital contributions prevents spin-down hybridization in both interfaces. The lack of hybridization between Sn and CrSTe is due to the absence of Sn-pz orbitals in the maxima of the SnC valence band as shown in the SI, Fig. S8 and hence, no magnetism is induced in Sn. However, no such correlation between hybridization and the contribution of px and py orbitals is observed in the two heterostructures. The Te atom shows a significant contribution of px and py orbitals around the Fermi level, but no hybridization in the Te interface heterostructure is observed. Although both spins of electrons contribute to the bands at the Fermi level in both heterostructures, it is the interfacial atom and its pz orbital contribution that dominate in determining the strength and possibility of interlayer hybridization during the formation of a heterostructure. Based on these results, we propose that the contribution of pz orbitals at the Fermi level of spin-polarized interfacial atoms governs interfacial hybridization. Furthermore, asymmetric pz-up and pz-down orbital contributions at the Fermi level are crucial for introducing spin polarization and magnetism in non-magnetic materials through interfacial hybridization.
This proposed mechanism of pz orbital mediated interfacial hybridization is schematically illustrated in Fig. 4(c–e). Fig. 4(c) schematically shows that when the magnetic system (A) contributes pz orbitals to the electronic band around the Fermi level, then these pz orbitals undergo interfacial hybridization with the electronic state of another material (B) when a heterostructure is formed between the two materials (A and B). In the figure, A and B schematically represent the electronic profile of two materials A and B, whereas A/B schematically represents the electronic profile of the heterostructure of A and B. In Fig. 4(c), the red line in A/B represents a new electronic state, which is not present in A or B and originates due to the interfacial hybridization between the pz orbitals of A and B. In contrast, there is no pz orbital around the Fermi level of A in Fig. 4(d). Therefore, there is no new electronic state in the heterostructure between A and B, which implies an absence of interfacial hybridization. Fig. 4(d) schematically demonstrates that the presence of pz orbitals is essential for interfacial hybridization, which is hypothesized from the results of the study. Fig. 4(e) shows that material A makes a pz-up electronic contribution around the Fermi level, while there is no pz-down contribution. Consequently the pz-up orbital hybridizes with the electronic state of B and a new state is generated for the up band. However, due to the absence of a pz-down orbital, no hybridization occurs and hence no new electronic state is generated for the down bands, which results in a spin polarized band for the material B in the heterostructure A/B. Fig. 4(e) schematically demonstrates the induced spin splitting in the non-spin polarized B system due to the presence of pz-up and the absence of pz-down orbitals around the Fermi level in system A. This explains the asymmetric magnetic effect of CrSTe on SnC in which the contribution of pz-up and pz-down sub-orbitals is asymmetric around the Fermi level in different interfaces.
To validate the proposed interfacial orbital-dependent spin-asymmetric behavior in the heterostructures, the charge redistribution profiles of both heterostructures were analyzed. Since interfacial hybridization is linked to charge transfer, higher charge transfer is expected for electrons with strong hybridization. The total, spin-up, and spin-down charge density differences for CrTeS/SnC and CrSTe/SnC are shown in Fig. 5(a–c) and (d–f). From the figures, it is evident that the charge transfer from SnC to the interfacial region is asymmetric for spin-up and spin-down charges in CrTeS/SnC. In CrTeS/SnC, spin-up charge transfer occurs from SnC (particularly C) to CrSTe due to strong spin-up hybridization at the Fermi level, while spin-down charge transfer is negligible due to the absence of hybridization. In contrast, CrSTe/SnC shows symmetric but minimal charge transfer for both spin channels, as confirmed by Bader charge analysis58–61 in Table 1. This minimal transfer is due to the lack of hybridization in both spins for CrSTe/SnC. The Bader analysis also shows significant spin-up charge transfer in CrTeS/SnC, which supports the proposed orbital hybridization mechanism. The change in charge density (Δρ) due to the formation of a heterostructure is calculated by subtracting the total Bader charge within the Bader volume of each atomic species in the pristine system from the Bader charges of the corresponding layers of the heterostructure. A positive value of (Δρ) represents the accumulation of charge in that layer, while a negative value represents a depletion of charge from that layer.
| System | Δρ (total) (e) | Δρ (up) (e) | Δρ (down) (e) |
|---|---|---|---|
| CrTeS/SnC | |||
| CrSTe | 0.1681 | 0.0979 | 0.0703 |
| SnC | −0.1681 | −0.1847 | 0.0165 |
| CrSTe/SnC | |||
| CrSTe | 0.0424 | 0.0250 | 0.0174 |
| SnC | −0.0424 | −0.0181 | −0.0244 |
Furthermore, since there is small lattice mismatch between CrSTe and SnC, to assess the impact of lattice matching on induced magnetism, we applied in-plane compressive and tensile strains ranging from −3% to +3% by adjusting the in-plane lattice constant as shown in the SI, Fig. S9. Tensile strain gradually enhances induced magnetism and spin splitting, while compressive strain suppresses them as shown in Fig. 5(g–l). These variations of induced magnetism align with the variation of pz orbital contributions at the Fermi level of CrSTe's interfacial atoms under strain. As pz-up orbital contributions increase or decrease, induced magnetism in the SnC layer follows a similar trend. This supports our hypothesis of the pz dependency in interfacial hybridization induced magnetic proximity effect.
Collectively, the figures and analyses reveal a magnetic proximity effect due to the spin-dependent interfacial hybridization controlled by atomic sub-orbitals of interfacial atoms. The observed interface-dependent asymmetric orbital hybridization in the two heterostructures arises from the asymmetric contribution of pz orbitals by CrSTe's interfacial atoms to the electronic band at the Fermi level. These interface and spin selectivities reveal that the presence or absence of a contribution of pz interfacial orbitals at the Fermi level determines the possibility of the presence or absence of hybridization in the heterostructure. When pz interfacial orbitals contribute, strong hybridization generates a new conducting state; otherwise, no hybridization occurs. These observations lead us to the proposed mechanism of interfacial hybridization, which states that the asymmetric contribution of pz-up and pz-down atomic sub-orbitals of the interfacial atom in a heterostructure is the principal driving factor of the interfacial hybridization induced magnetic proximity effect. These insights enable interface engineering of heterostructures by selecting materials with desired interfacial orbital contributions for application purposes.
The code of Quantum Espresso used in this work is open source code and publicly available.
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