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Tailoring magnetic characteristics of phosphorene by the doping of Ce and Ti: A DFT study
Accepted Manuscript Tailoring magnetic characteristics of phosphorene by the doping of Ce and Ti: A DFT study Fayyaz Hussain, Muhammad Imran, Muhammad Atif Sattar PII:
S1386-9477(17)31865-9
DOI:
10.1016/j.physe.2018.04.024
Reference:
PHYSE 13118
To appear in:
Physica E: Low-dimensional Systems and Nanostructures
Received Date: 5 December 2017 Revised Date:
6 April 2018
Accepted Date: 18 April 2018
Please cite this article as: F. Hussain, M. Imran, M.A. Sattar, Tailoring magnetic characteristics of phosphorene by the doping of Ce and Ti: A DFT study, Physica E: Low-dimensional Systems and Nanostructures (2018), doi: 10.1016/j.physe.2018.04.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Tailoring magnetic characteristics of phosphorene by the doping of Ce and Ti: A DFT study Fayyaz Hussaina, Muhammad Imranb, Muhammad Atif Sattarc* a
Materials Simulation Research Laboratory (MSRL), Department of Physics, BahauddinZakariya University Multan Pakistan, 60800 Department of Physics, Govt. College University Faisalabad, Pakistan
c
Department of Physics, The Islamia University of Bahawalpur, Pakistan
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Abstract
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Phosphorene, a two-dimensional elemental material, has attracted increasing attention owing
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to its fascinating characteristics. All calculations have been performed with the help of density functional theory (DFT) based on generalized gradient approximation method. In this work, we have explored the occurrence of magnetic moments in the non-magnetic phosphorene due to the substitution of Ce and Ti dopants. In the presence of Ce and Ti impurity atoms at up or down (dn) positions along the zigzag direction, phosphorene exhibits
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unique magnetic characteristics. The substitution of Ce-Ce or Ti-Ti couple in phosphorene has revealed ferromagnetic and half-metallic characteristics, whereas Ce-Ti couple substitution has shown weak magnetic behavior. On the other hand, the substitution of Ce at up and dn positions, neither have shown magnetic nor half metallic behavior. For Ti doping
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at up and dn positions, both have revealed a ferromagnetic behavior. These findings grant a
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productive ground for future spintronics applications based on phosphorene.
Keywords: 2D material, Doping; DFT; ferromagnetic, half-metallicity, Phosphorene
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Introduction Two dimensional (2D) crystals such as graphene, MoS2 as well as silicene are a focus of plenty of interest in the technology because of their numerous fascinating properties, rich physics and possibility of integration into next-generation electronic and energy conversion devices which arise due to their reduction of dimension and size [1].
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Instead of their own bulk counterparts, the optical, electronic, mechanical, as well as magnetic properties associated with 2D materials, could be very easily customized via the use of external strain, through presenting defects or even through stacking several layers from the same or perhaps diverse 2D materials. Lately, a brand new and also promising 2D
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semiconductor, Phosphorene, a growing star for the world of material sciences, is a 2D monolayer with puckered honeycomb framework extracted from bulk black phosphorous.
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Distinctive from graphene and MoS2, typically, spotless phosphorene provides unique properties which rely upon the thickness of the layer, direct band gap, high mobility of electrons and non-magnetic characteristics at room temperature which makes it a fantastic perspective in several applications, including optoelectronics and also electronic devices in order to quantum transportation [2].
Atomically slender 2D structures, possessing many intriguing properties because of
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the lowered size and dimensions, have got driven extraordinary loyalty to the research community [3]. In 2004, the breakthrough associated with monolayer graphene through Geim and Novoselov, it is possible to be able to exfoliate 2D components along with distinctive as
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well as stimulating physical properties [4]. In a recent couple of years, a semiconducting family of group-VA monolayers (arsenene, antimonene and bismuthene) have got enticed substantial consideration because of their interesting physical properties. Specifically,
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between these kinds of group-VA nanosheets, Sb and As present semi metallic properties inside their bulk kind whilst semi-conductive feature inside their 2D counterparts. Lately, monolayers associated with transition metal dichalcogenides, MoS2 as well as graphene have got lured impressive consideration because of their unusual optical, mechanical, thermal and electronic properties that are lacking within their bulk counterparts [8]. Their productive applications in electronic gadgets, on the other hand, are limited by a number of implicit deficiencies, for example, like the insufficient bandgap in graphene, or comparatively lower mobility inside MoS2, which encourage researchers to continue to find alternative 2D materials with electronic and magnetic properties [1, 9-10]. Luckily, presently there can be
ACCEPTED MANUSCRIPT found a lot of unexplored 2D materials that display various magnetic as well as electronic properties [4, 11 & 12]. In 1914, considering the breakthrough associated with phosphorus, the idea still did not find deemed by the experts because of its formidable toxicity as well as structural instability [1, 9]. Presently, a brand new 2D material known as phosphorene has been
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separated efficiently from black phosphorus bulk by mechanized exfoliation [13]. It offers band gap of (0. 59~2 eV) that is considerably bigger than its bulk mass (0. 3 eV) as well as a higher range of mobility of electrons at room temperature (up to 1000 cm2 V-1 s-1) [14 & 15]. The band gap of phosphorene highly relies upon the number of layers as well as strain within
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the layers that makes it better than graphene regarding of appliances applications. Phosphorene distinctive geometrical layer framework discloses extreme anisotropy within optical as well as transportation properties [16].
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Experts have a continual objective to attain controlled magnetism within nonmagnetic 2D pristine materials that may assist in the use of this kind of materials in recording media, magnetic inks, and spintronic devices. Even as understand that almost all 2D materials mainly present non-magnetic behavior, Just like graphene and MoS2, phosphorene usually are not anticipated to present magnetism. Consequently, diverse strategies are already introduced
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to tune and induce the magnetic properties of 2D materials. A number of factors to be considered i.e doping of impurity atoms, vacancy defects, and also substitutional doping may be efficiently used for the induced magnetization [13, 17]. A straightforward and also natural solution to introduce magnetism is adding adsorbates which have permanent magnetic
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moments, for instance, 3d transition-metal adatoms, on the outside surface of phosphorene. In fact, adatoms-decorated graphene has been viewed as a promising candidate pertaining to
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spintronic devices. Theoretically, substantially doped phosphorene uncovered many remarkable optical, electronic as well as magnetic attributes [18-22]. Thus, there exists a significant dependence on extensive notion with the ferromagnetism within 2D materials, the essential basic aspect in the spintronic applications [23]. Optoelectronic applications demand materials equally tuned to aim photons and also capable of exchange carriers, thus fresh 2D semiconductors together with band gaps and higher motilities tend to be extremely preferred. With this respect, it is of great impact to comprehend the electronic and magnetic behaviors of Ti & Ce-atom embellished phosphorene. Considering the fact that the dependable control of magnetic states is the effective use of the magnet nanostructures, it is also essential to build up a highly effective method to control the magnetism of the Ti & Ce decorated phosphorene system. In this theoretical research work, we present a systematic
ACCEPTED MANUSCRIPT first-principles study of the electronic and magnetic properties of Ti & Ce atom-decorated phosphorene. The outcomes display that due to the existence of the lone pair electrons on P within phosphorene, all the Ti and Ce can strongly bond to the phosphorene sheet along with very substantial binding energies. Furthermore, Ti and Ce atom-decorated phosphorene display fascinating magnetic properties, which mainly arise from the exchange splitting of Ti
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and Ce 3d orbitals.
Computational technique
All calculations are carried out within plane-wave DFT by employing the Vienna ab initio simulation package (VASP) [24 & 25]. The generalized gradient approximation (GGA)
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with the Perdew, Burke, and Ernzerhof (PBE) of function and projector augmented wave (PAW) potential is selected in all these DFT calculations [26-28, 29 & 30]. The 2D puckered
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hexagonal honeycomb phosphorene is modeled from the supercell which contains a total number of 64 atoms. The vacuum surface is set to be 14 Å for the 2D system along cdirection. Various combinations of doping of Ti and Ce impurities have been chosen and effect of doped element and position of substitution on the magnetic response of phosphorene monolayer. The typical Ce-Ce coupled phosphorene cell with their respective first nearest neighbors distance is shown in figure 1. The convergence test for both systems of total
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energy with respect to the electron wave function is expanded using plane waves with a cut off energy of 400 eV. The ionic position, cell volume and lattice parameters of the system are fully relaxed with conjugate gradient method until the Hellmann Feynman forces are smaller
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than 0.02 eV/Å and the energy convergence criteria are met with 1×10-5eV. Hybrid Functional corrections (HSE 06) [31] have been applied to get more accurate band gap. The popular scheme for this calculation is Monkhorst Pack (MP) [32, 33] which is applied for k-
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point sampling. The MP grid was chosen to be 5×5×9 for all the calculations.
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monolayer.
Results and discussion
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Figure 1: (a) to (g) showing Ce and Ti doping at various possible sites in the phosphorene
In order to find out the electronic distribution with energy, we analyzed the electronic density of states (DOS) and partial density of states (PDOS) [34]. Figure (2 & 3-9)
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respectively show the total DOS and PDOS of substituted Ce and Ti atoms substituted at various possible sites in the phosphorene monolayer. The Fermi level (EF) represented by a dotted line is set at E = 0 eV. Here the upper panel (blue) represents majority spin while the
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lower panel (red) represents minority spin.
In order to analyze the impact of each dopant, we investigated the DOS and PDOS of
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an impurity-doped phosphorene by following their electronic configuration which is as P (1s2 2s22p63s2 3p3); Ti (1s2 2s2 2p6 3s2 3p64s2 3d2); Ce (1s2 2s2 2p6 3s2 3p6 4s2 3d10 5s2 5p6 4d106s2 5d1 4f1). The valence bands of Ce, Ti, and phosphorene are composed of 5d, 3d, and 3porbital localized states respectively and the remaining electrons are artificially constrained to be core states and not allowed to interact with the remaining electrons. The resulting DOS for all configurations is shown in figure 2.
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Figure 2: The spin-polarized DOS of Ce-Ce, Ti-Ti, Ce-Ti, Ce-up, Ti-up, Ce- dn, and Ti- dn
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respectively. The vertical dotted line represents EF which is set at E = 0 eV.
From figure 2 it is clear that Ti-up, Ti-dn and Ce-Ti couple doped systems show weak
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magnetic behavior. Ce-up and Ce-dn neither show magnetic nor half metallic behavior. However, due to the spin polarization of the majority and minority spin channels crossing the EF, Ce-Ce and Ti-Ti couple doped systems show magnetic as well as half metallic behavior.
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The interaction of dopants and host atomic orbitals, valence band and conduction band results in the formation of bonding and antibonding states due to which magnetic and half metallic character is observed. These results indicate that each impurity doping has its own bonding characteristics.
When Ce or Ti atom is substituted in phosphorene, it replaces phosphorene atom and makes chemical bonding with the valence electrons. The remaining unpaired electrons in the 3p-orbital of hosted phosphorene atoms around the dopants give the total magnetic moment. The total magnetic moments and the calculated total spin-polarized energies are shown in Table 1.
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0.989 0.001 0.989 0.001 1.100 1.300 0.009
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2.277 2.371 2.711 2.371 2.711 2.394 2.506 2.747
Total magnetic moment (µB)
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Pure Phosphorene Ti(dn) Ce(dn) Ti(up) Ce(up) Ti-Ti Ce-Ce Ce-Ti
Spinpolarized energies Esp (eV) 88.00 87.16 88.00 87.16 89.77 87.96 89.53
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Doping element
Bond length Å
In the case of Ti-dn substituted system the total calculated magnetic moment is (0.989µ B). Ti itself mainly contributes towards total magnetic moment while exhibiting a magnetic moment of (0.591µ B) as shown in figure 3. Furthermore, Ti-dn doped system does
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not show half metallic behavior as observed from DOS. None of the nearest neighboring (nn) atoms of phosphorene contribute to the total magnetic moment each carrying magnetic moment of (-0.005 µ B) and (-0.001 µ B) respectively. This behavior can also be clearly
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observed from PDOS results shown in figure 3(a) and (b) plots.
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Figure 3: The spin-polarized PDOS of Ti-dn doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn atoms of Ti-dn.
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For Ce-dn decorated phosherene system, the total calculated magnetic moment is (0.001µ B) and the Ce itself contributes towards total magnetic moment having a magnetic moment of (0.832µ B) as shown in figure 4. Furthermore, Ce-dn doped system does not show
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half metallic behavior, which can be confirmed from DOS plot in figure 2. The PDOS of nn phosphorene atoms, can be observed from figure 4 ( a & b) and further they have magnetic
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moments of (-0.008µ B) and (-0.009 µ B) respectively. Therefore, nn atoms do not have an active role in the magnetic behavior of Ce-dn doped phosphorene monolayer.
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Figure 4: The spin-polarized PDOS of Ce-dn doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ce-dn.
In the case of Ti-up substituted phosphorene, the total calculated magnetic moment is (0.989µ B). Here the Ti itself does not contribute towards total magnetic moment and exhibit non-magnetic behavior having a magnetic moment of (-0.006µ B) as shown in figure 5.
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Furthermore, Ti-up doped system does not show half metallic behavior, as observed from DOS plot in figure 2. The nn phosphorene atom (a) carry out the magnetic moment of (0.591
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µ B). It shows the main contribution for supporting magnetic behavior, as in figure 5(a). The nn phosphorene atom does not exhibit significant contribution for magnetic behavior, as can be seen from figure 5 (b) and is also evident from its magnetic moment (-0.011µ B).
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Figure 5: The spin-polarized PDOS of Ti-up doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ti-up.
For the Ce-up substituted system, the total calculated magnetic moment is (0.001µ B) showing week magnetic behavior. The Ce itself does not contribute towards total magnetic
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moment by exhibiting non-magnetic behavior with the magnetic moment of (-0.001 µ B) as in figure 6. The nn phosphorene atom (a) have a major share in the total magnetic moment, can
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be seen from figure 6 (a). There is a spin polarization of majority spin channel near EF, having a magnetic moment of (0.832 µ B). It contributes to the total magnetic moment of Ceup doped phosphorene monolayer as shown in Figure 6. The nn phosphorene atom does not significantly contribute to magnetic behavior as in Figure 6 (b).
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Figure 6: The spin-polarized PDOS of Ce-up doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ce-up.
The spin-polarization result of the total magnetic moment for Ti-Ti couple substituted in phosphorene monolayer is 1.100µ B. This finding demonstrates that the magnetic moments are aligned in the similar direction showing ferromagnetic coupling between the dopant and
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the neighboring phosphorene atoms. This is depicted by DOS plot as it is evident that spinpolarized peak of majority spin channel near EF. Further Ti-Ti couple doped system shows
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half metallic behavior due to the minority spin channel near EF as observed from DOS plot. Additionally, Ti at the dn position mainly contribute (0.004 µ B) towards the total magnetic moment and Ti at up position does not take part in the magnetic properties by showing nonmagnetic character (-0.002µ B) as obvious from figure 7. The one of nn phosphorene atom (a) of Ti-dn shown in plot (d) mainly contributes towards magnetic behavior by imparting magnetic moment of (0.021 µ B). The contribution of all other nn phosphorene atoms is negligible this behavior can be revealed from figure 7 (a, b, c and d). The share of atoms (a), (b), (c) and (d) in the total magnetic moment is (-0.002 µ B), (-0.002 µ B), (-0.002 µ B) and (0.002 µ B) respectively.
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Figure 7: The spin-polarized PDOS of Ti-Ti doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ti-up and (c) and (d) shows PDOS of the nn atoms of Ti-dn.
The total magnetic moments for Ce-Ce couple substituted in phosphorene monolayer is calculated to be 1.300µ B. Further Ce-Ce couple doped system shows half metallic behavior due to the minority spin channel near EF. The Ce at the up position contributes towards the
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total magnetic moment (0.002 µ B) and Ce at dn position show non-magnetic nature (-0.001
µ B) as shown in figure 8. Each nn phosphorene atom of Ce-up also contributes towards
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magnetic properties having magnetic moments of (0.002µ B) and (0.001µ B) respectively as in figure 8 (a and b). While nn phosphorene atom of Ce-dn does not contribute significantly towards total magnetic moment as can be seen from figure 8 (c and d).
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Figure 8: The spin-polarized PDOS of Ce-Ce doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ce-up and (c) and (d) shows PDOS of the nn atoms of Ce-dn.
For Ce-Ti couple substitution, the total calculated magnetic moment is (0.009 µ B)
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which is very weak because there is no majority spin channel. Relatively Ti contributes towards the total magnetic moment as compared to Ce as they have magnetic moments of (0.114 µ B) and (0.010 µ B) respectively (in figure 9). The nn phosphorene atoms do not
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support the magnetic characteristics, as they have magnetic moments of (0.003 µ B), (0.002
µ B), (0.003 µ B) and (0.002 µ B) respectively. Interaction of majority and minority spin channel also supports the argument of the weak contribution of nn atoms as shown in figure 9 (a, b, c and d), respectively. Furthermore, Ce-Ti couple substitution does not show half metallic behavior that can be confirmed by figure 2 of DOS plot.
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Figure 9: The spin-polarized PDOS of Ce-Ti doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ti and (c) and (d) shows PDOS of the nn atoms of Ce
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Conclusion: This work demonstrates the magnetic behavior of 2D phosphorene with the help of total spinpolarized energies, magnetic moment, DOS and PDOS. The effect of substitution of Ce and Ti impurities at various possible sites in phosphorene along the zigzag direction has been observed. In case of Ti-up and Ti-dn, both systems exhibited ferromagnetic behavior. It is
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found that by substituting Ce-Ce and Ti-Ti couple, the induced magnetic moments of the dopants and neighboring phosphorene atoms have aligned in the similar direction which gives rise to ferromagnetic as well as half metallic behavior. The Ce-Ti couple substitution has
ACKNOWLEDGEMENTS
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depicted extremely weak ferromagnetic characteristics.
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This work is carried out in the Department of Physics Bahauddin Zakariya University Multan Pakistan.
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Highlights • The electronic and magnetic properties of Ti & Ce atom-decorated phosphorene explored using DFT method.
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• Occurrence of magnetic moments in the non-magnetic phosphorene due to the substitution of Ce and Ti dopants. • Phosphorene exhibits unique magnetic characteristics due to the presence of Ce and Ti impurity atoms along the zigzag direction.
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• The substitution of Ce-Ce or Ti-Ti couple in phosphorene has revealed ferromagnetic and halfmetallic characteristics.
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• Ti and Ce atom-decorated phosphorene display fascinating magnetic properties, which mainly arise from the exchange splitting of Ti and Ce 3d orbitals.
S1386-9477(17)31865-9
DOI:
10.1016/j.physe.2018.04.024
Reference:
PHYSE 13118
To appear in:
Physica E: Low-dimensional Systems and Nanostructures
Received Date: 5 December 2017 Revised Date:
6 April 2018
Accepted Date: 18 April 2018
Please cite this article as: F. Hussain, M. Imran, M.A. Sattar, Tailoring magnetic characteristics of phosphorene by the doping of Ce and Ti: A DFT study, Physica E: Low-dimensional Systems and Nanostructures (2018), doi: 10.1016/j.physe.2018.04.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Tailoring magnetic characteristics of phosphorene by the doping of Ce and Ti: A DFT study Fayyaz Hussaina, Muhammad Imranb, Muhammad Atif Sattarc* a
Materials Simulation Research Laboratory (MSRL), Department of Physics, BahauddinZakariya University Multan Pakistan, 60800 Department of Physics, Govt. College University Faisalabad, Pakistan
c
Department of Physics, The Islamia University of Bahawalpur, Pakistan
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Abstract
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Phosphorene, a two-dimensional elemental material, has attracted increasing attention owing
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to its fascinating characteristics. All calculations have been performed with the help of density functional theory (DFT) based on generalized gradient approximation method. In this work, we have explored the occurrence of magnetic moments in the non-magnetic phosphorene due to the substitution of Ce and Ti dopants. In the presence of Ce and Ti impurity atoms at up or down (dn) positions along the zigzag direction, phosphorene exhibits
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unique magnetic characteristics. The substitution of Ce-Ce or Ti-Ti couple in phosphorene has revealed ferromagnetic and half-metallic characteristics, whereas Ce-Ti couple substitution has shown weak magnetic behavior. On the other hand, the substitution of Ce at up and dn positions, neither have shown magnetic nor half metallic behavior. For Ti doping
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at up and dn positions, both have revealed a ferromagnetic behavior. These findings grant a
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productive ground for future spintronics applications based on phosphorene.
Keywords: 2D material, Doping; DFT; ferromagnetic, half-metallicity, Phosphorene
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Introduction Two dimensional (2D) crystals such as graphene, MoS2 as well as silicene are a focus of plenty of interest in the technology because of their numerous fascinating properties, rich physics and possibility of integration into next-generation electronic and energy conversion devices which arise due to their reduction of dimension and size [1].
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Instead of their own bulk counterparts, the optical, electronic, mechanical, as well as magnetic properties associated with 2D materials, could be very easily customized via the use of external strain, through presenting defects or even through stacking several layers from the same or perhaps diverse 2D materials. Lately, a brand new and also promising 2D
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semiconductor, Phosphorene, a growing star for the world of material sciences, is a 2D monolayer with puckered honeycomb framework extracted from bulk black phosphorous.
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Distinctive from graphene and MoS2, typically, spotless phosphorene provides unique properties which rely upon the thickness of the layer, direct band gap, high mobility of electrons and non-magnetic characteristics at room temperature which makes it a fantastic perspective in several applications, including optoelectronics and also electronic devices in order to quantum transportation [2].
Atomically slender 2D structures, possessing many intriguing properties because of
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the lowered size and dimensions, have got driven extraordinary loyalty to the research community [3]. In 2004, the breakthrough associated with monolayer graphene through Geim and Novoselov, it is possible to be able to exfoliate 2D components along with distinctive as
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well as stimulating physical properties [4]. In a recent couple of years, a semiconducting family of group-VA monolayers (arsenene, antimonene and bismuthene) have got enticed substantial consideration because of their interesting physical properties. Specifically,
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between these kinds of group-VA nanosheets, Sb and As present semi metallic properties inside their bulk kind whilst semi-conductive feature inside their 2D counterparts. Lately, monolayers associated with transition metal dichalcogenides, MoS2 as well as graphene have got lured impressive consideration because of their unusual optical, mechanical, thermal and electronic properties that are lacking within their bulk counterparts [8]. Their productive applications in electronic gadgets, on the other hand, are limited by a number of implicit deficiencies, for example, like the insufficient bandgap in graphene, or comparatively lower mobility inside MoS2, which encourage researchers to continue to find alternative 2D materials with electronic and magnetic properties [1, 9-10]. Luckily, presently there can be
ACCEPTED MANUSCRIPT found a lot of unexplored 2D materials that display various magnetic as well as electronic properties [4, 11 & 12]. In 1914, considering the breakthrough associated with phosphorus, the idea still did not find deemed by the experts because of its formidable toxicity as well as structural instability [1, 9]. Presently, a brand new 2D material known as phosphorene has been
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separated efficiently from black phosphorus bulk by mechanized exfoliation [13]. It offers band gap of (0. 59~2 eV) that is considerably bigger than its bulk mass (0. 3 eV) as well as a higher range of mobility of electrons at room temperature (up to 1000 cm2 V-1 s-1) [14 & 15]. The band gap of phosphorene highly relies upon the number of layers as well as strain within
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the layers that makes it better than graphene regarding of appliances applications. Phosphorene distinctive geometrical layer framework discloses extreme anisotropy within optical as well as transportation properties [16].
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Experts have a continual objective to attain controlled magnetism within nonmagnetic 2D pristine materials that may assist in the use of this kind of materials in recording media, magnetic inks, and spintronic devices. Even as understand that almost all 2D materials mainly present non-magnetic behavior, Just like graphene and MoS2, phosphorene usually are not anticipated to present magnetism. Consequently, diverse strategies are already introduced
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to tune and induce the magnetic properties of 2D materials. A number of factors to be considered i.e doping of impurity atoms, vacancy defects, and also substitutional doping may be efficiently used for the induced magnetization [13, 17]. A straightforward and also natural solution to introduce magnetism is adding adsorbates which have permanent magnetic
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moments, for instance, 3d transition-metal adatoms, on the outside surface of phosphorene. In fact, adatoms-decorated graphene has been viewed as a promising candidate pertaining to
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spintronic devices. Theoretically, substantially doped phosphorene uncovered many remarkable optical, electronic as well as magnetic attributes [18-22]. Thus, there exists a significant dependence on extensive notion with the ferromagnetism within 2D materials, the essential basic aspect in the spintronic applications [23]. Optoelectronic applications demand materials equally tuned to aim photons and also capable of exchange carriers, thus fresh 2D semiconductors together with band gaps and higher motilities tend to be extremely preferred. With this respect, it is of great impact to comprehend the electronic and magnetic behaviors of Ti & Ce-atom embellished phosphorene. Considering the fact that the dependable control of magnetic states is the effective use of the magnet nanostructures, it is also essential to build up a highly effective method to control the magnetism of the Ti & Ce decorated phosphorene system. In this theoretical research work, we present a systematic
ACCEPTED MANUSCRIPT first-principles study of the electronic and magnetic properties of Ti & Ce atom-decorated phosphorene. The outcomes display that due to the existence of the lone pair electrons on P within phosphorene, all the Ti and Ce can strongly bond to the phosphorene sheet along with very substantial binding energies. Furthermore, Ti and Ce atom-decorated phosphorene display fascinating magnetic properties, which mainly arise from the exchange splitting of Ti
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and Ce 3d orbitals.
Computational technique
All calculations are carried out within plane-wave DFT by employing the Vienna ab initio simulation package (VASP) [24 & 25]. The generalized gradient approximation (GGA)
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with the Perdew, Burke, and Ernzerhof (PBE) of function and projector augmented wave (PAW) potential is selected in all these DFT calculations [26-28, 29 & 30]. The 2D puckered
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hexagonal honeycomb phosphorene is modeled from the supercell which contains a total number of 64 atoms. The vacuum surface is set to be 14 Å for the 2D system along cdirection. Various combinations of doping of Ti and Ce impurities have been chosen and effect of doped element and position of substitution on the magnetic response of phosphorene monolayer. The typical Ce-Ce coupled phosphorene cell with their respective first nearest neighbors distance is shown in figure 1. The convergence test for both systems of total
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energy with respect to the electron wave function is expanded using plane waves with a cut off energy of 400 eV. The ionic position, cell volume and lattice parameters of the system are fully relaxed with conjugate gradient method until the Hellmann Feynman forces are smaller
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than 0.02 eV/Å and the energy convergence criteria are met with 1×10-5eV. Hybrid Functional corrections (HSE 06) [31] have been applied to get more accurate band gap. The popular scheme for this calculation is Monkhorst Pack (MP) [32, 33] which is applied for k-
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point sampling. The MP grid was chosen to be 5×5×9 for all the calculations.
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monolayer.
Results and discussion
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Figure 1: (a) to (g) showing Ce and Ti doping at various possible sites in the phosphorene
In order to find out the electronic distribution with energy, we analyzed the electronic density of states (DOS) and partial density of states (PDOS) [34]. Figure (2 & 3-9)
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respectively show the total DOS and PDOS of substituted Ce and Ti atoms substituted at various possible sites in the phosphorene monolayer. The Fermi level (EF) represented by a dotted line is set at E = 0 eV. Here the upper panel (blue) represents majority spin while the
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lower panel (red) represents minority spin.
In order to analyze the impact of each dopant, we investigated the DOS and PDOS of
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an impurity-doped phosphorene by following their electronic configuration which is as P (1s2 2s22p63s2 3p3); Ti (1s2 2s2 2p6 3s2 3p64s2 3d2); Ce (1s2 2s2 2p6 3s2 3p6 4s2 3d10 5s2 5p6 4d106s2 5d1 4f1). The valence bands of Ce, Ti, and phosphorene are composed of 5d, 3d, and 3porbital localized states respectively and the remaining electrons are artificially constrained to be core states and not allowed to interact with the remaining electrons. The resulting DOS for all configurations is shown in figure 2.
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Figure 2: The spin-polarized DOS of Ce-Ce, Ti-Ti, Ce-Ti, Ce-up, Ti-up, Ce- dn, and Ti- dn
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respectively. The vertical dotted line represents EF which is set at E = 0 eV.
From figure 2 it is clear that Ti-up, Ti-dn and Ce-Ti couple doped systems show weak
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magnetic behavior. Ce-up and Ce-dn neither show magnetic nor half metallic behavior. However, due to the spin polarization of the majority and minority spin channels crossing the EF, Ce-Ce and Ti-Ti couple doped systems show magnetic as well as half metallic behavior.
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The interaction of dopants and host atomic orbitals, valence band and conduction band results in the formation of bonding and antibonding states due to which magnetic and half metallic character is observed. These results indicate that each impurity doping has its own bonding characteristics.
When Ce or Ti atom is substituted in phosphorene, it replaces phosphorene atom and makes chemical bonding with the valence electrons. The remaining unpaired electrons in the 3p-orbital of hosted phosphorene atoms around the dopants give the total magnetic moment. The total magnetic moments and the calculated total spin-polarized energies are shown in Table 1.
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0.989 0.001 0.989 0.001 1.100 1.300 0.009
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2.277 2.371 2.711 2.371 2.711 2.394 2.506 2.747
Total magnetic moment (µB)
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Pure Phosphorene Ti(dn) Ce(dn) Ti(up) Ce(up) Ti-Ti Ce-Ce Ce-Ti
Spinpolarized energies Esp (eV) 88.00 87.16 88.00 87.16 89.77 87.96 89.53
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Doping element
Bond length Å
In the case of Ti-dn substituted system the total calculated magnetic moment is (0.989µ B). Ti itself mainly contributes towards total magnetic moment while exhibiting a magnetic moment of (0.591µ B) as shown in figure 3. Furthermore, Ti-dn doped system does
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not show half metallic behavior as observed from DOS. None of the nearest neighboring (nn) atoms of phosphorene contribute to the total magnetic moment each carrying magnetic moment of (-0.005 µ B) and (-0.001 µ B) respectively. This behavior can also be clearly
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observed from PDOS results shown in figure 3(a) and (b) plots.
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Figure 3: The spin-polarized PDOS of Ti-dn doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn atoms of Ti-dn.
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For Ce-dn decorated phosherene system, the total calculated magnetic moment is (0.001µ B) and the Ce itself contributes towards total magnetic moment having a magnetic moment of (0.832µ B) as shown in figure 4. Furthermore, Ce-dn doped system does not show
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half metallic behavior, which can be confirmed from DOS plot in figure 2. The PDOS of nn phosphorene atoms, can be observed from figure 4 ( a & b) and further they have magnetic
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moments of (-0.008µ B) and (-0.009 µ B) respectively. Therefore, nn atoms do not have an active role in the magnetic behavior of Ce-dn doped phosphorene monolayer.
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Figure 4: The spin-polarized PDOS of Ce-dn doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ce-dn.
In the case of Ti-up substituted phosphorene, the total calculated magnetic moment is (0.989µ B). Here the Ti itself does not contribute towards total magnetic moment and exhibit non-magnetic behavior having a magnetic moment of (-0.006µ B) as shown in figure 5.
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Furthermore, Ti-up doped system does not show half metallic behavior, as observed from DOS plot in figure 2. The nn phosphorene atom (a) carry out the magnetic moment of (0.591
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µ B). It shows the main contribution for supporting magnetic behavior, as in figure 5(a). The nn phosphorene atom does not exhibit significant contribution for magnetic behavior, as can be seen from figure 5 (b) and is also evident from its magnetic moment (-0.011µ B).
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Figure 5: The spin-polarized PDOS of Ti-up doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ti-up.
For the Ce-up substituted system, the total calculated magnetic moment is (0.001µ B) showing week magnetic behavior. The Ce itself does not contribute towards total magnetic
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moment by exhibiting non-magnetic behavior with the magnetic moment of (-0.001 µ B) as in figure 6. The nn phosphorene atom (a) have a major share in the total magnetic moment, can
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be seen from figure 6 (a). There is a spin polarization of majority spin channel near EF, having a magnetic moment of (0.832 µ B). It contributes to the total magnetic moment of Ceup doped phosphorene monolayer as shown in Figure 6. The nn phosphorene atom does not significantly contribute to magnetic behavior as in Figure 6 (b).
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Figure 6: The spin-polarized PDOS of Ce-up doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ce-up.
The spin-polarization result of the total magnetic moment for Ti-Ti couple substituted in phosphorene monolayer is 1.100µ B. This finding demonstrates that the magnetic moments are aligned in the similar direction showing ferromagnetic coupling between the dopant and
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the neighboring phosphorene atoms. This is depicted by DOS plot as it is evident that spinpolarized peak of majority spin channel near EF. Further Ti-Ti couple doped system shows
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half metallic behavior due to the minority spin channel near EF as observed from DOS plot. Additionally, Ti at the dn position mainly contribute (0.004 µ B) towards the total magnetic moment and Ti at up position does not take part in the magnetic properties by showing nonmagnetic character (-0.002µ B) as obvious from figure 7. The one of nn phosphorene atom (a) of Ti-dn shown in plot (d) mainly contributes towards magnetic behavior by imparting magnetic moment of (0.021 µ B). The contribution of all other nn phosphorene atoms is negligible this behavior can be revealed from figure 7 (a, b, c and d). The share of atoms (a), (b), (c) and (d) in the total magnetic moment is (-0.002 µ B), (-0.002 µ B), (-0.002 µ B) and (0.002 µ B) respectively.
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Figure 7: The spin-polarized PDOS of Ti-Ti doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ti-up and (c) and (d) shows PDOS of the nn atoms of Ti-dn.
The total magnetic moments for Ce-Ce couple substituted in phosphorene monolayer is calculated to be 1.300µ B. Further Ce-Ce couple doped system shows half metallic behavior due to the minority spin channel near EF. The Ce at the up position contributes towards the
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total magnetic moment (0.002 µ B) and Ce at dn position show non-magnetic nature (-0.001
µ B) as shown in figure 8. Each nn phosphorene atom of Ce-up also contributes towards
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magnetic properties having magnetic moments of (0.002µ B) and (0.001µ B) respectively as in figure 8 (a and b). While nn phosphorene atom of Ce-dn does not contribute significantly towards total magnetic moment as can be seen from figure 8 (c and d).
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Figure 8: The spin-polarized PDOS of Ce-Ce doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ce-up and (c) and (d) shows PDOS of the nn atoms of Ce-dn.
For Ce-Ti couple substitution, the total calculated magnetic moment is (0.009 µ B)
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which is very weak because there is no majority spin channel. Relatively Ti contributes towards the total magnetic moment as compared to Ce as they have magnetic moments of (0.114 µ B) and (0.010 µ B) respectively (in figure 9). The nn phosphorene atoms do not
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support the magnetic characteristics, as they have magnetic moments of (0.003 µ B), (0.002
µ B), (0.003 µ B) and (0.002 µ B) respectively. Interaction of majority and minority spin channel also supports the argument of the weak contribution of nn atoms as shown in figure 9 (a, b, c and d), respectively. Furthermore, Ce-Ti couple substitution does not show half metallic behavior that can be confirmed by figure 2 of DOS plot.
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Figure 9: The spin-polarized PDOS of Ce-Ti doped phosphorene monolayer. The vertical dotted line represents EF which is set at E = 0 eV. Where (a) and (b) shows PDOS of the nn
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atoms of Ti and (c) and (d) shows PDOS of the nn atoms of Ce
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Conclusion: This work demonstrates the magnetic behavior of 2D phosphorene with the help of total spinpolarized energies, magnetic moment, DOS and PDOS. The effect of substitution of Ce and Ti impurities at various possible sites in phosphorene along the zigzag direction has been observed. In case of Ti-up and Ti-dn, both systems exhibited ferromagnetic behavior. It is
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found that by substituting Ce-Ce and Ti-Ti couple, the induced magnetic moments of the dopants and neighboring phosphorene atoms have aligned in the similar direction which gives rise to ferromagnetic as well as half metallic behavior. The Ce-Ti couple substitution has
ACKNOWLEDGEMENTS
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depicted extremely weak ferromagnetic characteristics.
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This work is carried out in the Department of Physics Bahauddin Zakariya University Multan Pakistan.
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Highlights • The electronic and magnetic properties of Ti & Ce atom-decorated phosphorene explored using DFT method.
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• Occurrence of magnetic moments in the non-magnetic phosphorene due to the substitution of Ce and Ti dopants. • Phosphorene exhibits unique magnetic characteristics due to the presence of Ce and Ti impurity atoms along the zigzag direction.
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• The substitution of Ce-Ce or Ti-Ti couple in phosphorene has revealed ferromagnetic and halfmetallic characteristics.
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• Ti and Ce atom-decorated phosphorene display fascinating magnetic properties, which mainly arise from the exchange splitting of Ti and Ce 3d orbitals.