Investigation of the insulator to half-metal transition in Cr-doped ZnO at low temperature (19 K) wurtzite structure
Keywords:
Wurtzite structure, Density functional theory (DFT), Ferromagnetism, Half-metal, Local spin density approximation (LSDA)Abstract
The structural, electronic and magnetic properties of pure and Cr doped ZnO with a low temperature (19 K) wurtzite structure were calculated employing the density functional theory (DFT) as implemented in the tight-binding linearized-muffin-tin orbital (TB-LMTO) method. Pure ZnO is observed a nonmagnetic insulator, in which all the Zn-3d orbitals are found occupied and electrons are perfectly paired in each orbital causing nonmagnetic nature of pure ZnO. But Cr doping in ZnO significantly changes its structural, electronic and magnetic properties. This material encounters nonmagnetic insulator to ferromagnetic half-metal with minute structural distortions at 50% Cr substitution (Zn0.5Cr0.5O) for Zn. It is revealed in this study that Zn0.5Cr0.5O is metallic for majority spin species and insulating for minority spin species with a semiconducting gap ~3.5 eV. Due to the strong electron correlation effect, three Cr-t2g orbitals become fully occupied by three Cr-3d electrons while remaining single electron is shared by two eg ¬orbitals in the close vicinity of the Fermi level. This sharing of the single electron by two eg orbitals is responsible for the metallic behaviour of Zn0.5Cr0.5O. The parallel alignment of unpaired electrons in the Cr-3d orbitals is responsible for ferromagnetism of this material.References
Anderson, O. K. (1975). Linear methods in band theory. Physical Review B, 12 3060.
Anderson, O. K. & Jepsen, O. (1984). Explicit, First-Principles Tight-Binding Theory. Physical Review Letters, 53:2571.
Ballif, C. (2011). Nanomoulding of transparent zinc oxide electrodes for efficient light trapping in solar cells. Nature Photonics, 5: 535–538.
Battaglia, C., Escarre, J., So ̈derstro ̈m, K., Charriere, M., Despeisse, M. et al. (2009). Crossed zinc oxide nanorods for ultraviolet radiation detection. Sensors Actuators A: Physical, 150: 184–187.
Chen, Y., Xu, X. L., Zhang, G. H., Xue, H. & Ma, S. Y. (2010). Blue shift of optical band gap in Er-doped ZnO thin films deposited by direct current reactive magnetron sputtering technique. Physica E, 42:1713−1716.
Dietl, T., Ohno, H., Matsukura, F., Cibert, J. & Ferrand, D. (2000). Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors. Science 287 :1019-1022.
Djurisi, A. B., Ng, A. M. C. & Chen, X. Y. (2010). ZnO nanostructures for optoelectronics: material properties and device applications. Progress in Quantum Electronics, 34:191–259.
Gao, P. X. & Wang, Z. L. (2005). Nanoarchitctures of semiconducting and piezoelectric zinc oxide. Journal of Applied Physics, 97 (044304):1-7.
Hohenberg, P. & Kohn, W. (1964). Inhomogeneous Electron Gas. Physical Review, 136: B864.
Iqbal, A., Mahmood, A., Khan, T. M. & Ahmed, E. (2013). Structural and optical properties of Cr doped ZnO crystalline thin films deposited by reactive electron beam evaporation technique. Progress in Natural Science: Materials International 23(1): 64–69.
Jin, Z., Fukumura, T., Kawasaki, M., Ando, K., Saito, H et al. (2009). First Principles Calculations of Electronic Band Structure and Optical Properties of Cr-Doped ZnO. The Journal of Physical Chemistry C, 113:8460-8464.
Kohn, W. Sham, L. J. (1965). Self-Consistent Equations Including Exchange and Correlation Effects. Physical Review B, 140: A1133.
Lin, Y. C., Hsu, C. Y., Hung, S. K., Chang, C. H. & Wen, D. C. (2012). The structural and optoelectronic properties of Ti-doped ZnO thin films prepared by introducing a Cr buffer layer and post annealing. Applied Surface Science 258:9891– 9895.
Murakami, M., Matsumoto, Y., Hasegawa, T. & Koinuma, H. (2001). High throughput fabrication of transition-metal-doped epitaxial ZnO thin films: A series of oxide-diluted magnetic semiconductors and their properties. Applied Physics Letters, 78:3824.
Osuch, K., Lombardi, E. B. & Gebicki, W. (2006). First principles study of ferromagnetism in Ti0.0625Zn0.9375O. Physical Review B, 73:075202.
Perdew, J. P. & Wang, Y. (1992). Accurate and simple analytic representation of the electron-gas correlation energy. Physical Review B, 45:13244.
Rasouli, S. & Moeen, S. J. (2011). Combustion synthesis of co-doped zinc oxide nanoparticles using mixture of citric acid–glycine fuels. Journal Alloys and Compound, 509, 1915–1919.
Roberts, B. K., Pakhomov, A. B., Shutthanandan, V. S. & Krishnan, K. M. (2005). Ferromagnetic Cr-doped ZnO for spin electronics via magnetron sputtering. Journal of Applied Physics, 97:10D310.
Sato, K. & Katayama, Y. H. (2002). First principles materials design for semiconductor spintronics. Semiconductor Science and Technology, 17:367-376.
Shah, A. H., Ahamed, M. B., Neena, D., Mohmed, F. & Iqbal, A. (2014). Investigations of optical, structural and antibacterial properties of Al–Cr dual-doped ZnO nanostructure. Journal of Alloys and Compounds, 606:164–170.
Ueda, K., Tabata, H. & Kawai, T. (2001). Magnetic and electric properties of transition-metal-doped ZnO films. Applied Physics Letters, 79:988.
Vidya Sagar, R. & Baddhudus, R. (2010). Synthesis and magnetic behaviour of Mn:ZnO nanocrystalline powders. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 75 (4): 1218–1222.
Yi, J., Lee, J. M. & Park, W. (2011). Vertically aligned ZnO nanorods and graphene hybrid architectures for high-sensitive flexible gas sensors. Sensors and Actuators B: Chemical 155: 264–269.
Yılmaz, S., Parlak, M., Ozcan, S., Altunbas, M., McGlynn, E. & Bacaksiz, E. (2011). Structural, optical and magnetic properties of Cr doped ZnO microrods prepared by spray pyrolysis method. Applied Surface Science, 257:9293– 9298.
Yoshio, K. Onodera, A., Satop, H., Sakagami, N. & Yamashita, H. (2001). Crystal structure of ZnO:Li at 293 K and 19 K by X-ray Diffraction. Ferroelectrics, 264:133-138.
Zheng, B. J., Lian, J. S. & Jiang, Q. (2011). Highly transparent and conductive Zn0.86Cd0.11In0.03O thin film prepared by pulsed laser deposition. Journal of Superconductivity and Novel Magnetism, 24:1627−1632.
