First-principles calculations on the mechanical electronic magnetic and optical properties of two-dimensional Janus Cr 2TeX X P As Sb monolayers Qiuyue Ma1Wenhui Wan1Yanfeng Ge1Yingmei Li1and Yong Liu1a

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First-principles calculations on the mechanical, electronic, magnetic and optical

properties of two-dimensional Janus Cr2TeX (X= P, As, Sb) monolayers

Qiuyue Ma,1Wenhui Wan,1Yanfeng Ge,1Yingmei Li,1and Yong Liu1, a)

State Key Laboratory of Metastable Materials Science and Technology &

Key Laboratory for Microstructural Material Physics of Hebei Province,

School of Science, Yanshan University, Qinhuangdao 066004,

China

Janus materials possess extraordinary physical, chemical, and mechanical properties

caused by symmetry breaking. Here, the mechanic properties, electronic structure,

magnetic properties, and optical properties of Janus Cr2TeX (X= P, As, Sb) mono-

layers are systematically investigated by the density functional theory. Janus Cr2TeP,

Cr2TeAs, and Cr2TeSb are intrinsic ferromagnetic (FM) half-metals with wide spin

and half-metallic gaps. The Curie temperature ( Tc) of these monolayers are about

583, 608, and 597 K, respectively by Monte Carlo simulations based on the Heisen-

berg model. Additionally, it has been found that Cr2TeX (X= P, As, Sb) monolayers

still exhibit FM half-metallic properties under biaxial strain ranging from -6% to 6%.

At last, the Cr2TeP monolayer has a higher absorption coeﬃcient than the Cr2TeAs

and Cr2TeSb monolayers in the visible region. The results predict that Janus Cr2TeX

(X= P, As, Sb) monolayers with novel properties have good potential for applications

in future nanodevices.

a)Electronic mail: yongliu@ysu.edu.cn

arXiv:2210.09686v4 [cond-mat.mtrl-sci] 6 May 2023

The discovery of two-dimensional (2D) honeycomb structures of graphene is considered

one of the most important discoveries in the ﬁeld of physics and materials science1. The

unique outstanding physical and chemical properties of graphene have led to an upsurge in

the study of 2D materials. Then, a large number of 2D layered materials have been reported,

including hexagonal boron nitride2,3, transition metal dichalcogenides (TMDs)4–6, silicene7–9

have shown great potential for various applications. 2D Janus monolayers show novel phys-

ical and chemical properties, such as piezoelectric polarization10, Rashba eﬀect11,12, and

catalytic performance13,14, which open up new possibilities in the ﬁeld of 2D materials. The

Janus In2SeTe is synthesized by substituting one layer of Se atoms with Te atoms to break

the inversion symmetry of InSe, which possesses transport characteristics that are superior

to InSe monolayer15. Similarly, the Janus In2SSe monolayer has an indirect-direct bandgap

transition due to broken vertical symmetry16. 2D Janus PdXO (X= S, Se, Te) monolayers

with high electron mobility have good potential for applications in future nanodevices17. For

Janus TMDs materials, the MXY (M = Mo, W; X, Y = S, Se, Te; X 6= Y) monolayers show

excellent intrinsic dipole and piezoelectric eﬀects18.

Recently, many 2D magnetic materials have been predicted, such as CrI319, Cr2Ge2Te6

20, V3X821, Cr2NX2(X = O, F, OH)22, and M2SeTe (X= Ga, In)23. Meanwhile, recent works

also conﬁrm that many Janus magnetic materials have excellent properties, such as Cr2I3X3

(X = F, Cl, Br)24, FeXY (X, Y = Cl, Br, and I, X 6= Y)25, XGaInY (X, Y;= S, Se and Te)26.

2D Janus monolayers possess extraordinary physical and chemical characteristics, which

have potential applications in 2D nanoscale spintronic devices. Half-metals with one spin

channel conducting and the other semiconducting ﬁlter the current into a single spin channel

for realizing pure spin transport, generation, and injection. The FeCl2is experimentally

known to exist in a monolayer form and is a classical material with half-metallic properties

27, but its Curie temperature (Tc) is only 17 K, which greatly aﬀects its application in

spintronics due to its relatively low Tc. In recent years, it has been recognized that the

half-metallic materials have exposed high Tcas a result of the strong exchange interaction

driven by charge carriers28. Theoretical studies have predicted many 2D half-metals with

high Tc, Fe2Si for 780 K29, MnAsS4for 740 K30, MnP and MnAs for 495 K and 711 K31, and

Mn2AsP monolayer for 557 K32. 2D half-metals, which have abundant charge carriers, are

expected to be much higher Tcvalues than 2D magnetic semiconductors. The outstanding

attributes of half-metals are potentially promising for the fabrication of future nanodevices.

In this work, the structural characteristics, mechanical, electronic properties, magnetic

properties, and optical properties of Janus Cr2TeX (X= P, As, Sb) monolayers have been

studied based on the ﬁrst-principles calculations. The results show that the Janus Cr2TeX

(X= P, As, Sb) monolayers are intrinsic ferromagnetic half-metals with wide half-metallic

gaps and spin gaps. The predicted Tcof Janus Cr2TeX (X= P, As, Sb) monolayers reached

up to 583, 608, and 597 K. Janus Cr2TeX (X= P, As, Sb) monolayers still retain their half-

metallic properties and the FM natures are robust against biaxial strain in the range of -6%

to 6%. At last, we displayed their optical properties, the Cr2TeSb has a higher absorption

coeﬃcient and lower energy-loss coeﬃcient in the ultraviolet region. Our calculations indi-

cate that Janus Cr2TeX (X= P, As, Sb) monolayers are potentially promising for spintronic

devices.

The present calculations were performed by adopting the Vienna ab initio simulation

package (VASP) based on the density functional theory (DFT)33–35. The generalized gra-

dient approximation (GGA) functional of Perdew, Burke, and Ernzerhof (PBE) was used

to investigate the exchange-correlation function36. We used the spin-dependent GGA plus

Hubbard U to deal with the strongly correlated interactions of the transition metal Cr el-

ement, the Hubbard U term of 3 eV was used for Cr37. The plane-wave cutoﬀ energy was

chosen to be 500 eV. Monkhorst-Pack special k-point mesh is 9 ×9×1 for the Brillouin

zone integration38. The convergence criteria for energy and force during the relaxation of

the structures were set to 10−6eV and 0.01 eV/˚

A. The vertical vacuum spacing of 20 ˚

A was

used to eliminate interactions between images. Phonon dispersions of the studied materials

were obtained using the phonopy code based on the density functional perturbation theory

(DFPT)39.

The crystal structure of Janus Cr2TeX (X= P, As, Sb) monolayers is shown in Fig.1(a).

One Cr layer is sandwiched between the X layer and Te layer. The lattice constants of

Janus Cr2TeX monolayers increase from 4.50 of Cr2TeP to 4.65 ˚

A of Cr2TeSb due to the

increase in the size of the X atom. The calculated structure parameters of Janus Cr2TeX

(X= P, As, Sb) monolayers are summarized in Table I. As shown in Fig.1(b), four typical

magnetically coupled conﬁgurations in the 2 ×1×1 supercell are considered to study

the ground state of the Cr2TeX ( X = P, As, Sb) monolayers. Four spin conﬁgurations

conﬁrm that the FM coupling is more energetically stable than antiferromagnetic(AFM)

coupling. Additionally, the non-magnetic state can be neglected due to the energy diﬀerence

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First-principlescalculationsonthemechanical,electronic,magneticandopticalpropertiesoftwo-dimensionalJanusCr2TeX(X=P,As,Sb)monolayersQiuyueMa,1WenhuiWan,1YanfengGe,1YingmeiLi,1andYongLiu1,a)StateKeyLaboratoryofMetastableMaterialsScienceandTechnology&KeyLaboratoryforMicrostructuralMaterialPhysicsofHeb...

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First-principles calculations on the mechanical electronic magnetic and optical properties of two-dimensional Janus Cr 2TeX X P As Sb monolayers Qiuyue Ma1Wenhui Wan1Yanfeng Ge1Yingmei Li1and Yong Liu1a.pdf

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First-principles calculations on the mechanical electronic magnetic and optical properties of two-dimensional Janus Cr 2TeX X P As Sb monolayers Qiuyue Ma1Wenhui Wan1Yanfeng Ge1Yingmei Li1and Yong Liu1a

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