Synergetic Effect of Substitutional Dopants and Sulfur Vacancy in

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Synergetic Effect of Substitutional Dopants and Sulfur Vacancy in Modulating the Ferromagnetism of MoS2 Nanosheets Wei Hu, Hao Tan, Hengli Duan, Guinan Li, Na Li, Qianqian Ji, Ying Lu, Yao Wang, Zhihu Sun, Fengchun Hu, Chao Wang, and Wensheng Yan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b09165 • Publication Date (Web): 06 Aug 2019 Downloaded from pubs.acs.org on August 6, 2019

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ACS Applied Materials & Interfaces

Synergetic Effect of Substitutional Dopants and Sulfur Vacancy in Modulating the Ferromagnetism of MoS2 Nanosheets Wei Hu,†, Hao Tan,†, Hengli Duan,† Guinan Li,† Na Li,† Qianqian Ji,† Ying Lu,† Yao Wang,† Zhihu Sun,*,† Fengchun Hu,† Chao Wang,*,‡ and Wensheng Yan*,† †

National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, P. R. China ‡

Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui 230031, P. R. China

ABSTRACT: The activation and modulation of the magnetism of MoS2 nanosheets are critical to the development of their application in next-generation spintronics. Here, we report a synergetic strategy to induce and modulate the ferromagnetism of the originally nonmagnetic MoS2 nanosheets. A two-step experimental method was used to simultaneously introduce substitutional V dopants and sulfur vacancy (Vs) in MoS2 nanosheets host, showing an air-stable and adjustable ferromagnetic response at room temperature. The ferromagnetism could be modulated by varying the content of Vs through Ar plasma irradiation of different period, with a maximum saturation magnetization of 0.011 emu g-1 reached at the irradiation time of 6 seconds (s). Experimental characterizations and first-principles calculations suggest that the adjustable magnetization is attributed to the synergetic effect of the substitutional V dopants and Vs in modulating the band structure of MoS2 nanosheets, resulting from the strong hybridization between the V 3d state and Vs-induced impurity bands. This work suggests that synergetic effect of substitutional V atoms and Vs is a promising route for tuning the magnetic interactions in two-dimensional nanostructures.

KEYWORDS: Magnetic MoS2 nanosheets; substitutional dopants; sulfur vacancy; synergetic effect; strong hybridization

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INTRODUCTION Two-dimensional (2D) Van der Waals materials such as graphene,1,2 phosphorene,3 silicene,4 hexagonal boron nitride5 and transition metal dichalcogenides (TMDs)6-10 are at the forefront of research due to the wealth of unusual physical and chemical properties for various applications, especially in spintronics.11,12 These materials have long spin lifetime and/or strong spin-orbit coupling induced spin-momentum locking, which make the spin injection and detection with 2D materials a new trend and an interesting topic.12 Among a diversity of 2D materials, MoS2 nanosheets have attracted great interest because of their tunable charge-carrier types, high on/off ratio, high carrier mobilities, and ultralow standby power dissipation.9, 13-15 These features make MoS2 nanosheets very important candidates for applications in low-dimensional spintronics. However, in many cases the property of MoS2 nanosheets is inherited from the intrinsic property of the 3D-material MoS2, which hinders the obtainment of desired property that is absent in their bulk counterpart, and hence limits the application field. For instance, the nonmagnetic property of normal MoS2 nanosheets has hampered its practical applications in next-generation spintronic devices. Therefore, how to effectively induce and manipulate the magnetism of MoS 2 nanosheets is a prerequisite for applying the MoS2 nanosheets into spintronics, but it remains a challenge. To obtain ferromagnetic MoS2 nanosheets and other low dimensional materials, various methods have been proposed, such as substitutional doping,16,17 introducing vacancy defects,18 strain,19 passivation,20 zigzag edge,21 and so forth. Among these methods, doping alien atoms and generating vacancy defects have proved to be facial strategies. For example, numerous studies have shown that magnetism in MoS2 nanosheets could be triggered by Mn, Co, Fe, Ni, Cu, Ti and Cd doping.16,

22-24

However, this method could hardly manipulate the magnetic strength, as the doped transition metal atoms have limited solid solubility in MoS2 nanosheets. Theoretical calculations by Zheng et al. have predicted that the ground state of unstrained doped MoS2 system with vacancy defect of Mo neighboring three disulfur pairs (VMoS6) is magnetic,25 but it is difficult to construct this structure experimentally. Hence,


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experimental approaches to effectively modulate the magnetism are still to be pursued. Previous studies have indicated that the band structure of MoS2 nanosheets could be modulated by either the transition metal (TM) dopants or the vacancy defects,16,26-29 and the impurity levels induced by these two methods have a strong interaction with each other.25,28 This is in analogy to the traditional ZnO and GaN-based dilute magnetic semiconductors, for which first-principles calculations and experiments have predicted that, the strategies of codoping with cation-cation, anion-cation, especially cation-defect, can effectively regulate their magnetic properties.30-33 Therefore, simultaneously introducing substitutional TM doping and vacancy defects should provide a chance to modulate the magnetism of MoS2 nanosheets. Recently, there were studies that ion irradiation with low energy is a controllable and simple way to induce sulfur vacancies (Vs) into layered MoS2 samples.34-36 Moreover, due to the similar atomic radii of vanadium (1.32 Å) and Mo (1.36 Å) atoms, stable substitutional doping can be achieved without generating impurity phases under irradiation. Motivated by the above consideration, we anticipate that the V substitutionally doped MoS2 nanosheets along with Vs could be an effective strategy to modulate the magnetism of MoS2 nanosheets. In this work, a synergetic strategy of introducing V-doping and Vs is employed to activate and modulate the ferromagnetism of the originally nonmagnetic MoS2 nanosheets. Substitutional doping of vanadium into MoS2 is achieved in a hydrothermal synthesis, and the Vs can be introduced by argon (Ar) plasma irradiation. A combination of spectroscopic techniques and first-principles calculations uncover that the band structure of pure MoS2 nanosheets is modified by this strategy, giving rise to the modulated magnetic performance of the nanosheets. This deliberately designed structure suggests an avenue to manipulate the magnetism or other desired properties in doped 2D TMDs materials.

RESULTS AND DISCUSSION The V-doped MoS2 nanosheets with S vacancies (Vs) were synthesized through a two-step experimental strategy, where the initial V-doped MoS2 (here after called



V/MoS2) nanosheets were formed through hydrothermal reaction at a temperature of 200 °C. Then the obtained V/MoS2 nanosheets were transferred onto a clear cylindrical cavity and treated by a mild Ar plasma irradiation to create Vs. The experimental details are described in the Supporting Information. The morphology and crystal structure of the as-synthesized product can be directly observed from the transmission electron microscopy (TEM) image as shown in Figure 1a and Figure S1 in the Supporting Information. The nanosheets with uniform lateral size in the range of 100−150 nm have faint contrast, revealing the ultrathin nature of the sample. The High-resolution transmission electron microscopy (HRTEM) image in the inset shows the distinct lattice fringes of 0.27 nm with 60°intersection angle, corresponding to the (010) and (100) planes of 2H-MoS2. This point is also supported by the X-ray diffraction (XRD) patterns (Figure S2a). The top left shows a fast Fourier transform result of the region enclosed by the yellow square in the bottom left. It clearly shows a hexagonal lattice structure with a d-spacing of 0.274 and 0.162 nm, corresponding to the (100) and (010) planes of 2H-MoS2, respectively.37,38 The cross-sectional TEM image (Figure S1) indicates that the V/MoS2 nanosheets mainly have two to five atomic layer thicknesses. Moreover, there are no nanoparticles or large clusters of V in the HRTEM image, consistent with the XRD patterns showing no V-containing crystal phases. The Energy-dispersive X-ray spectroscopy (EDS) mapping images in Figure 1b indicate the homogeneous distribution of Mo, S and V atoms over the entire flake of nanosheet at a micrometer scale. Moreover, according to the inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis, the molar ratio of V/Mo in the V/MoS2 nanosheets is about 5.7 at%. Besides, the location of the V atoms can be revealed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) as shown in Figure 1c. There are some darker spots randomly distributed in the brighter white (Mo atoms) atomic columns (marked by yellow circles) with lower cross sectional intensity of the atom contrast (Figure 1d), indicating the V atoms occupy the positions of the Mo atoms. The V substitution is further confirmed by analysis of X-ray absorption near edge structure (XANES) (Figure 1f) spectra. The V K-edge XANES of V/MoS2 nanosheets


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Figure 1. (a) TEM image of the V/MoS2 nanosheets. Inset: HRTEM image and the fast Fourier transform result of the region enclosed by the yellow square. (b) EDS elemental mapping images, and (c) HAADF-STEM image of the V/MoS2 nanosheets. (d) The intensity profile of the selected area (blue rectangle) of the V/MoS2 nanosheets in (c). (e) XPS results of V/MoS2 nanosheets before and after Ar plasma irradiation. (f) Mo K-edge and V K-edge XANES spectra of the V/MoS2 nanosheets and the calculated spectra for the model structure: the substitutional V (VMo), as well as V K-edge XANES spectrum of the V/MoS2 nanosheets after Ar plasma irradiation. The inset displays the comparison of the intensity for the pre-edge peak A1. exhibits four characteristic peaks A, B, C and D, in analogy to those of Mo K-edge XANES (see detailed V K-edge XANES analysis in the Supporting Information). Furthermore, these spectral features can be well reproduced by our calculation using FEFF8.239 for substitutional V (VMo) in MoS2 nanosheets. The V L2,3-edge XANES (Figure S3) and the wavelet-transform (WT) analysis of the V K-edge EXAFS data (Figure S4) also indicate that the doped V atoms occupy the Mo lattice position in MoS2 and are in trigonal prismatic coordination environment. XPS measurements were also conducted to monitor the changes caused by Ar plasma irradiation. It is worthy to note that after the treatment by a mild Ar plasma irradiation for 6 s, the intensity corresponding to the S 2p characteristic peak is significantly reduced (Figure



1e), while the Mo 3d XPS (inset in Figure 1e) and V K-edge XANES spectra (Figure 1f) does not change significantly. This means that Ar plasma irradiation only creates Vs, while does not change the spatial occupations and valence of Mo ions and V dopants in the MoS2 lattice (see details in Figures S5-7 of the Supporting Information). Furthermore, a close inspection of the pre-edge peak A1 (5469 eV, inset in Figure 1f) indicates that the peak intensity is relatively weakened after Ar plasma irradiation, due to the transfer of residual electrons to V atoms after creation of Vs. These results show the successful synthesis of MoS2 nanosheets with substitutional V dopants and Vs by high temperature hydrothermal and successive Ar plasma irradiation. In order to clarify the effect of doped V atoms and the introduced Vs on the magnetic properties of MoS2 nanosheets, we measured the magnetizations curves (M−H) as a function of the applied magnetic field H (Figure 2a) at 300 K for the as-prepared MoS2, V/MoS2, and V/MoS2 with Vs (denoted as V/MoS2@6s hereafter) nanosheets. The well-defined hysteresis loop for V/MoS2 nanosheets indicates the room-temperature ferromagnetic behavior with a saturation magnetization of about 0.003 emu g-1, significantly higher than that of the weakly ferromagnetic MoS2 nanosheets.40 Interestingly, the saturation magnetization of V/MoS2 could be enhanced from 0.003 (1.310-3) to 0.011 (5.310-3) emu g-1 (μB V-1) after Ar plasma irradiation for 6 s with coercivity up to 47 Oe. Further, the magnetization (M−T) curves against temperature under field-cooling (FC) and zero-field-cooling (ZFC) mode (Figure S8) suggest that the V/MoS2@6s nanosheets have a Curie temperature (TC) above 350 K, and no superparamagnetic phase transition can be observed, excluding the possibility of V cluster. At the same time, Mott−Schottky measurements also showed that there are increased content of Vs in V/MoS2 nanosheets after Ar plasma irradiation, inferred from the significant decrease in the positive slope of the Mott−Schottky plots (Figure 2b) (see details in the Supporting Information). These results indicate that, as we expected, the introduction of Vs by Ar plasma irradiation can effectively enhance the magnetic properties of V/MoS2 nanosheets. In contrast, introducing Vs defect alone does not cause significant change in saturation magnetic moment of pure MoS2 (Figure S9a). Furthermore, for the V/MoS2@6s nanosheets, the


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Figure 2. (a) Magnetization vs. magnetic field (M-H) curves for MoS2, V/MoS2 and V/MoS2@6s nanosheets. The inset shows the zoom around low field region for better perception. (b) Mott−Schottky plots, and (c) Raman spectra for MoS2, V/MoS2 and V/MoS2@6s nanosheets. (d) Comparison of the magnetic signal changes of the V/MoS2 nanosheets upon Vs content with various irradiation time. The dashed lines serve to guide the eyes.

Raman spectrum (Figure 2c) does not show characteristic peaks corresponding to 1T-MoS2, further confirming that the enhanced saturation magnetization of V/MoS2 nanosheets is caused by the synergetic effect of the substitutional V atoms and the Vs, rather than by the phase transition introduced by Vs. Considering the V doping level (5.7 at%) in the MoS2 nanosheets with carrier concentration less than 1020 cm-3 calculated by magnetic-field-dependent Hall measurements, the room temperature ferromagnetism of V/MoS2 nanosheets could hardly be interpreted by the carrier induction mechanism. Alternatively, the bound magnetic polaron (BMP)41 model is a promising candidate (see details in Figure S10-11 of the Supporting Information). Based on the XPS measurement, we determined the Vs contnet in the initial V-doped MoS2 and the sample after Ar plasma irradiation for different times. The



results displayed in Figure 2d are close to those reported in literature.42,43 To better illustrate the dependence of the magnetic performance on the Vs content, we extracted the magnetic signals of the V/MoS2 nanosheets from the measured M-H curves (Figure S9b) and plot them against the Vs content in Figure 2d. Obviously, the saturation magnetization of V/MoS2 nanosheets does not increase monotonically with the Vs content; it reaches the maximum (0.011 emu g-1) at the irradiation time of 6 s with Vs content of about 6.4%. However, when the irradiation time is prolonged to 12 s, the saturation magnetization is dropped to 0.005 emu g-1. A similar phenomenon has been observed in conventional TM (Mn and Co) doped ZnO,44 because carriers bound around the highly concentrated Vs become mobile and destroy the ferromagnetic couplings caused by the magnetic mechanism of bound magnetic polaron (BMP). It is expected that the enhanced ferromagnetism can be observed in V/MoS 2 nanosheets with the further increase of Vs, but too high content of Vs may lead to the generation of 1T-MoS2. For deeper insights into the role of V dopants and Vs in tuning the magnetic behavior of MoS2 nanosheets, the electron paramagnetic resonance (EPR) and XANES spectra were combined to probe their local electronic structures. From the EPR spectra (Figure 3a), upon doping of V, an intense eight-lined signal as expected of a V(IV) is clearly observed, which comes from the interaction of V4+ electron spin with its nuclear spin of I = 7/2. The V(IV) can also be confirmed by the first-derivative of V K-edge XANES curves (Figure 3b), as the inflexion point of the peak (the maximum of the first derivative curve) matches exactly in position with that of the VO2 reference. This indicates the 4+ valence state of the V dopants substituting for the Mo sites. Each V4+ ion carries an extra magnetic moment of 1 B V-1 to the MoS2 nanosheets at room temperature; this is the fundamental reason for the enhanced magnetic moment of V/MoS2 in comparison to MoS2 nanosheets. After Ar plasma irradiation, the intensity of the eight-lined EPR signal is significantly enhanced, suggesting the intensified interaction between Vs and V4+ in addition to the increased Vs content. As shown in Figure 3c, with the introduction of Vs and V atoms, the Mo M2,3-edge XANES spectra MoS2 nanosheets are also changed significantly.


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EPR Intensity (a.u.)

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Figure 3. (a) EPR spectra of MoS2, V/MoS2, and V/MoS2@6s nanosheets. (b) First-derivative of V K-edge XANES curves for V/MoS2, V/MoS2@6s nanosheets, and vanadium oxides with various oxidation states. (c) Mo M-edge XANES spectra, and (d) UPS spectra for pure MoS2, V/MoS2 and V/MoS2@6s nanosheets.

The pure MoS2 nanosheets exhibit two characteristic peaks (M2 and M3) associated with the transitions from the Mo 3p core-level to the unoccupied 4d final state. After introduction of V atoms and Vs, the peak intensity of M3 decreases, which implies the redistributed electrons in Mo 4d levels. It is worth of note that the S K-edge XANES in Figure S12 also show an obvious change after introduction of the V dopants and Vs. This means that the valence bands of MoS2 is also changed, because the valence bands of MoS2 are mainly contributed by the hybridization of Mo 4d and S 3p states. To explicitly reflect this point, the valence band structure was further probed through ultraviolet photoelectron spectroscopy (UPS) as shown in Figure 3d. When the V atoms are solely doped into MoS2, the valence-band maximum (VBM) exhibits only a subtle change. Further, for the V/MoS2@6s nanosheets, the VBM is upshifted by 0.18



eV, indicating the changed valence bands due to electron redistribution near the Fermi level, which is induced by the shallow state of Vs close to the VB edge (seeing the in-gap band structure of MoS2-Vs as shown in Figure S11.45 These results verify the success of the synergetic effect of the substitutional V atoms and the Vs in modulating the band structure of MoS2 nanosheets. For an in-depth understanding of the origin of Vs in modulating the magnetism of V/MoS2 nanosheets, we employed the ABINIT software package to calculate the electronic structures of V/MoS2 with Vs (V/MoS2-Vs), as well as of pure MoS2, V/MoS2 and pure MoS2 with Vs (MoS2-Vs) for comparison (see calculation details in the Supporting Information). Theoretical calculations show that introducing Vs reduces slightly the band gap of V/MoS2, which is supported by the experimental UV-vis diffuse reflectance spectra (UV-Vis-DRS) in Figure S13. The obtained total and partial densities of states (DOS) and the spin density are shown in Figure 4a-d and Figure S14, respectively. Pure MoS2 exhibits symmetric spin-up and spin-down DOSs (Figure 4a), it in accordance with previous works.23 However, when substitutional V atoms and Vs are introduced individually, the DOSs of MoS2 nanosheets as shown in Figure 4b-c present significant changes. In the case of sole substitutional V doping (Figure 4b), the introduction of V atom modifies the energy band structure of MoS2, where the 3d energy levels of the spin-up and spin-down branches are unequally occupied, indicating the generation of magnetic states. In the case of sole introduction of Vs (Figure 4c), two impurity levels a and b, with the main Mo 4d character, are generated at the top of valence band and the bottom of conduction band, respectively. Interestingly, when V atoms and Vs coexist (Figure 4d), the energy levels introduced by V atoms are obviously hybridized with the impurity levels of Vs, and the impurity level b exhibits spin-splitting compared to the DOS when Vs is introduced separately. Therefore, according to the BMP model, the interaction between the V 3d level and the Vs-induced impurity level is the fundamental reason for the strong room-temperature ferromagnetism observed in the structure of V/MoS2 with Vs (V/MoS2-Vs). As shown in Figures 4e and 4f, the increase of Vs creates more bound magnetic polarons, causing more overlap between


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the bound magnetic polarons and V atoms providing magnetic moments. This intensifies the macroscopic magnetism of the V/MoS2 nanosheets and enhances the magnetic moment from ~0.003 to ~0.011 emu g-1 as experimentally observed. It is worth noting that if the content of Vs exceeds a certain threshold, the carriers bound around Vs will become no longer localized, which destroys the bound magnetic polarons and in return leads to a decrease in the saturation magnetization. This explains the experimental observations of the attenuated magnetic moment after a longer irradiation beyond 6 s (Figure 2d). Hence, taking into account the experimental and theoretical results, we may draw the conclusion that band engineering caused by the V/MoS2-Vs synergetic system is the underlying reason for tuning the magnetic behavior of the MoS2 nanosheets. Our theoretical calculations show the same spin polarization direction of Mo atom near the Vs as the V atom. This means that ferromagnetic successive spin polarizations (SSP-FMC)46 may also occur in our samples and contribute to the increase in saturation magnetization.

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antiferromagnetic pair

Figure 4. Calculated total and partial density of states for various model structures: (a) pure MoS2, (b) V/MoS2, (c) pure MoS2 with Vs (MoS2-Vs) and (d) V/MoS2 with Vs (V/MoS2-Vs). Schematic presentation of magnetic polarons before (e) and after (f) the introduction of Vs.



CONCLUSIONS In summary, we have used a two-step synergetic strategy to successfully introduce substitutionally doped V atoms and sulfur vacancy into MoS2 nanosheets and obtained ferromagnetism at room temperature. More interestingly, the ferromagnetism in the as-synthesized nanosheets could be modulated by adjusting the Ar plasma irradiation time, with a maximum saturation magnetization of 0.011 emu g-1 reached at the irradiation time of 6 s (Vs content of 6.4%). As shown by the detailed experimental characterizations and first-principles calculations, we propose that the observed robust ferromagnetism of V/MoS2 with Vs (V/MoS2-Vs) originates from the hybridization between the V 3d state and Vs-induced impurity bands. This work shows that the synergetic effect of the substitutional TM doping and vacancy defects could be an effective pathway for modulation of the magnetic behavior of 2D magnetic semiconductor materials.

EXPERIMENTAL SECTION Synthesis of MoS2 and V-doped MoS2 (V/MoS2) nanosheets. V/MoS2 nanosheets as synthesized through a one-pot chemical method. Firstly, 1mmol (NH4)6Mo7O24·4H2O, 30mmol thiourea, 0.16mmol Na3VO4 and 0.4g cetyl trimethyl ammonium bromide (CTAB) were dissolved in 40 mL deionized water and ultrasonicated to form a homogeneous solution. After ultrasonication for 2 h, the solution was transferred into a 50 ml stainless steel autoclave and maintained at 200 ℃ for 20 h. Then the reaction system was allowed to cool down to room temperature naturally. The obtained products were collected by centrifugation and washed with deionized water and ethanol and drying at 60 ℃ under vacuum. For comparison, the pure MoS2 nanosheets was synthesized by using 1mmol (NH4)6Mo7O24·4H2O, 30 mmol thiourea and 0.4g CTAB dissolved in 40 mL deionized water, the other processes were the same as those in the synthesis of MoS2. The formation of S vacancies (Vs) with different content on V/MoS2 nanosheets. To introduce different content of Vs into V/MoS2 nanosheets, an argon (Ar) plasma treatment was employed. Ar plasma was generated by a 5W RF (13.56 MHz) power,


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the obtained V/MoS2 nanosheets were uniformly dispersed in a plastic dish and placed at the center of the cylindrical cavity. The argon pressure in the cavity is 5 mTorr by flowing argon at 10 sccm and vacuum pumping. After that, the formation of Vs with different content on V/MoS2 nanosheets was carried out at room temperature by varying the Ar plasma irradiation time. The small RF power ensure a mild Ar plasma on the V/MoS2 surface, resulting in a controllable desulphurization process.

ASSOCIATED CONTENT Supporting Information Materials characterization, DFT calculation details, characterization of the Vs in the V/MoS2 nanosheets after Ar plasma irradiation, X-ray diffraction patterns, FTIR spectra, V L2,3-edge XANES spectra, wavelet transforms results, XPS survey spectra, STEM-EDS measurement, high-resolution XPS images of Mo 3d and S 2p for V/MoS2 nanosheets before and after Ar plasma irradiation, magnetization vs. magnetic field (M-H) curves, real and imaginary parts of dielectric constant of single-layer MoS2, band structure for single-layer MoS2 33 supercell with a Vs, Mo L3-edge and S K-edge XANES spectra, UV-Vis-DRS spectra, and spin density plots.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (Z.S.). *E-mail: [email protected] (C.W.). *E-mail: [email protected] (W.Y.). ORCID Zhihu Sun: 0000-0002-3898-969X Chao Wang: 0000-0002-3378-6594 Wensheng Yan: 0000-0001-6297-4589 Author Contributions The manuscript was written through contributions of all authors. All authors have



given approval to the final version of the manuscript. W. H. and H. T. contributed equally to this work.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants No.11435012, 11775225, U1632263, 21533007 and 11604341) and partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication. The authors would like to thank BSRF and NSRL for the synchrotron beamtime.

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Table of Contents overlapping polarons 6s

1.0

-2

M10 (emu/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3s

0.8 0.6

2s

9s 12s

0.4 0s T=300K

2

4 6 8 Vacancy Concentration (%)

10

isolated polarons


antiferromagnetic pair

Synergetic Effect of Substitutional Dopants and Sulfur Vacancy in

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