Electronic and Magnetic Properties of Co-doped Rb 2 Ni 3 S 4 Gang Bahadur Acharya Central Department of Physics Tribhuvan University, Kirtipur, Nepal Supervisor Dr. Madhav Prasad Ghimire Associate Professor October 20, 2020 October 20, 2020 1 / 13
Outline Introduction/Background Methodology and Computational tools Electronic and magnetic properties of Rb 2 Ni 3 S 4 Half metallicity in Co-doped Rb 2 Ni 3 S 4 Discussion and Conclusions October 20, 2020 2 / 13
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 a Figure: structure of kagome lattice. without losing energy at room a http://www.hfmphysics.com/2006/motif.htm temperature. October 20, 2020 3 / 13
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) October 20, 2020 4 / 13
Crystal structure Rb 2 Ni 3 S 4 Face centered-orthorhombic structure with the Figure: Ni ions constitute a Kagome space group Fmmm lattice. (69) Symmorphic space group lattice parameters: a = 5.90615070 ˚ A , b = 10.06449278 ˚ A , c = 13.43457036 ˚ A Figure: Crystal structure of Rb 2 Ni 3 S 4 . Angles : α = β = γ = (blue balls are Rb atoms, red balls are 90° Ni atoms and black balls are S atoms) October 20, 2020 5 / 13
Methodology and Computational tools Study electronic and magnetic properties of Rb 2 Ni 3 S 4 and Co-doped Rb 2 Ni 3 S 4 Density functional theory (DFT)calculation. Generalized gradient approximation (GGA) used for exchange correlation interaction. Full Potential Local Orbital (FPLO)code used for calculations. October 20, 2020 6 / 13
Results and Discussion Electronic and Magnetic Properties of Rb 2 Ni 3 S 4 2.0 1.0 Energy ε n (k) [eV] Nonmagnetic, ferromagnetic 0.0 ε F and antiferromagnetic −1.0 configuration. −2.0 Y T Z X Γ Γ Figure: Band structure of Rb 2 Ni 3 S 4 in Ground state is to be weak scalar relativistic. ferromagnetic. 2.0 1.0 Energy ε n (k) [eV] ε F 0.0 −1.0 −2.0 Γ Y T Z Γ X Figure: Band structure of Rb 2 Ni 3 S 4 in full relativistic. October 20, 2020 7 / 13
Results and Discussion Electronic and Magnetic Properties of Co-doped Rb 2 Ni 3 S 4 25.0 ↑ ↑ 15.0 Co−3d ↑ Co−3d ↑ 20.0 Co−3d ↓ Co−3d ↓ ↓ ↓ 10.0 15.0 PDOS (states/eV) 5.0 10.0 PDOS (states/eV) 0.0 5.0 −5.0 0.0 −10.0 −5.0 −15.0 −4.0 −2.0 0.0 2.0 4.0 Energy (eV) −10.0 15.0 −15.0 Ni−3d ↑ Ni−3d ↑ Ni−3d ↓ Ni−3d ↓ 10.0 −20.0 PDOS (states/eV) 5.0 −25.0 −4.0 −2.0 0.0 2.0 4.0 0.0 Energy (eV) −5.0 Figure: Density of states of Co-doped −10.0 −15.0 Rb 2 Ni 3 S 4 in scalar relativistic −4.0 −2.0 0.0 2.0 4.0 Energy (eV) 15.0 S−3p ↑ S−3p ↑ S−3p ↓ S−3p ↓ 10.0 Co-doped in the place of first PDOS (states/eV) 5.0 Ni. 0.0 −5.0 −10.0 Ground state is ferromagnetic. −15.0 −4.0 −2.0 0.0 2.0 4.0 Energy (eV) Figure: Partial Density of states of Co-doped Rb 2 Ni 3 S 4 in scalar relativistic. October 20, 2020 8 / 13
Results and Discussion Electronic and Magnetic Properties of Co-doped Rb 2 Ni 3 S 4 2.0 ↑ ↑ ↓ ↓ Half metallic ferromagnetism. 1.0 Energy ε n (k) [eV] ε F 0.0 magnetic moment 2.0µ B /unit −1.0 cell. −2.0 Γ Y T Z Γ X A 1 Figure: Band structure of Co-doped Rb 2 Ni 3 S 4 in scalar relativistic Ferromagnetism mainly derived from Co-3d spins. 2.0 1.0 Energy ε n (k) [eV] 0.0 ε F Strong hybridization between −1.0 Ni-3d and Co-3d orbitals. −2.0 Y T Z X A 1 Γ Γ Figure: Band structure of Co-doped Rb 2 Ni 3 S 4 in full relativistic October 20, 2020 9 / 13
Electronic and Magnetic Properties of Co-doped Rb 2 Ni 3 S 4 Fad band of Rb 2 Ni 2 CoS 4 fm GGA(SOC) 2.0 Kagome lattice materials can Rb4p Rb4p Co3d Co3d Ni3d Ni3d host flat band. S3p S3p 1.0 Energy ε n (k) [eV] With energy 0.36eV above the ε F 0.0 Fermi level. Electronic flat bands in −1.0 momentum space arising from −2.0 strong localization of Y T Z X Γ Γ electrons. Figure: Fad band structure of Co-doped Rb 2 Ni 3 CoS 4 in full relativistic October 20, 2020 10 / 13
Conclusions Parent materials Rb 2 Ni 3 S 4 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. October 20, 2020 11 / 13
Acknowledgment Assoc. Prof. Dr. Madhav Prasad Ghimire (Supervisor) CDP , Nepal PD Dr. Manuel Richter (Co-supervisor) IFW Dresden Prof. Dr. Binil Aryal (HOD) October 20, 2020 12 / 13
October 20, 2020 13 / 13
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