Electronic and Magnetic Properties of Co-doped Rb 2 Ni 3 S 4 Gang - - PowerPoint PPT Presentation

Electronic and Magnetic Properties of Co-doped Rb2Ni3S4

Gang Bahadur Acharya

Central Department of Physics Tribhuvan University, Kirtipur, Nepal Supervisor

• Dr. Madhav Prasad Ghimire

Associate Professor

October 20, 2020

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Outline Introduction/Background Methodology and Computational tools Electronic and magnetic properties of Rb2Ni3S4 Half metallicity in Co-doped Rb2Ni3S4 Discussion and Conclusions

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Introduction/Background

Kagome Metals

Kagome: Traditional Japanese woven bamboo pattern.

Japanese Word : Kago - Basket, Me - Eyes. Atoms of a conducting substances arranged in Kagome pattern - shows exotic electronic properties. Kagome lattice: Vertices and edges of tri-hexagonal tiling, each hexagon is surrounded by triangles. Importance : conduct electricity without losing energy at room temperature.

Figure: structure of kagome lattice.

a ahttp://www.hfmphysics.com/2006/motif.htm

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Introduction/Background

Half Metals

One spin channel metallic. Opposite spin channel insulating. Zero energy band gap superior electronic properties than non zero energy gap material. Importance: Practical applications in spintronics, electronics and sensors.

Figure: The electronic band structures of various classes of materials. 1

1(Wang et al., NPG Asia Mater. 2, 31, (2010)

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Crystal structure Rb2Ni3S4

Face centered-orthorhombic structure with the space group Fmmm (69) Symmorphic space group lattice parameters: a = 5.90615070 ˚ A, b = 10.06449278 ˚ A, c = 13.43457036 ˚ A Angles : α = β = γ = 90°

Figure: Ni ions constitute a Kagome lattice. Figure: Crystal structure of Rb2Ni3S4. (blue balls are Rb atoms, red balls are Ni atoms and black balls are S atoms)

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Methodology and Computational tools

Study electronic and magnetic properties of Rb2Ni3S4 and Co-doped Rb2Ni3S4 Density functional theory (DFT)calculation. Generalized gradient approximation (GGA) used for exchange correlation interaction. Full Potential Local Orbital (FPLO)code used for calculations.

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Results and Discussion

Electronic and Magnetic Properties of Rb2Ni3S4

Nonmagnetic, ferromagnetic and antiferromagnetic configuration. Ground state is to be weak ferromagnetic.

−2.0 −1.0 0.0 1.0 2.0 εF Γ Y T Z Γ X Energy εn(k) [eV]

Figure: Band structure of Rb2Ni3S4 in scalar relativistic.

−2.0 −1.0 0.0 1.0 2.0 εF Γ Y T Z Γ X

Energy εn(k) [eV]

Figure: Band structure of Rb2Ni3S4 in full relativistic.

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Results and Discussion

Electronic and Magnetic Properties of Co-doped Rb2Ni3S4

−25.0 −20.0 −15.0 −10.0 −5.0 0.0 5.0 10.0 15.0 20.0 25.0 −4.0 −2.0 0.0 2.0 4.0 PDOS (states/eV) Energy (eV) ↑ ↓ ↑ ↓

Figure: Density of states of Co-doped Rb2Ni3S4 in scalar relativistic

Co-doped in the place of first Ni. Ground state is ferromagnetic.

−15.0 −10.0 −5.0 0.0 5.0 10.0 15.0 −4.0 −2.0 0.0 2.0 4.0 PDOS (states/eV) Energy (eV) Co−3d ↑ Co−3d ↓ Co−3d ↑ Co−3d ↓ −15.0 −10.0 −5.0 0.0 5.0 10.0 15.0 −4.0 −2.0 0.0 2.0 4.0 PDOS (states/eV) Energy (eV) Ni−3d ↑ Ni−3d ↓ Ni−3d ↑ Ni−3d ↓ −15.0 −10.0 −5.0 0.0 5.0 10.0 15.0 −4.0 −2.0 0.0 2.0 4.0 PDOS (states/eV) Energy (eV) S−3p ↑ S−3p ↓ S−3p ↑ S−3p ↓

Figure: Partial Density of states of Co-doped Rb2Ni3S4 in scalar relativistic.

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Results and Discussion

Electronic and Magnetic Properties of Co-doped Rb2Ni3S4

Half metallic ferromagnetism. magnetic moment 2.0µB /unit cell. Ferromagnetism mainly derived from Co-3d spins. Strong hybridization between Ni-3d and Co-3d orbitals.

−2.0 −1.0 0.0 1.0 2.0 εF Γ Y T Z Γ X A1 Energy εn(k) [eV]

Figure: Band structure of Co-doped Rb2Ni3S4 in scalar relativistic

−2.0 −1.0 0.0 1.0 2.0 εF Γ Y T Z Γ X A1

Energy εn(k) [eV]

Figure: Band structure of Co-doped Rb2Ni3S4 in full relativistic

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Electronic and Magnetic Properties of Co-doped Rb2Ni3S4

Kagome lattice materials can host flat band. With energy 0.36eV above the Fermi level. Electronic flat bands in momentum space arising from strong localization of electrons.

−2.0 −1.0 0.0 1.0 2.0 εF Γ Y T Z Γ X Energy εn(k) [eV]

Fad band of Rb2Ni2CoS4 fm GGA(SOC)

Rb4p Co3d Ni3d S3p Rb4p Co3d Ni3d S3p

Figure: Fad band structure of Co-doped Rb2Ni3CoS4 in full relativistic

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Conclusions

Parent materials Rb2Ni3S4 is weak ferromagnetic in nature. Upon full replacement of Ni(1) by Co atom ferromagnetic half metallic state achieved. Strong hybridization between Ni 3d and Co 3d orbitals.

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Acknowledgment

• Assoc. Prof. Dr. Madhav Prasad Ghimire (Supervisor)

CDP , Nepal PD Dr. Manuel Richter (Co-supervisor) IFW Dresden

• Prof. Dr. Binil Aryal (HOD)

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