Moreover, substrate contribution to the magnetization and the weight of the material in the thin film samples are difficult to measure accurately. All these things may lead to different magnetization value than bulk sample. Interestingly, Matsuno et al . have explained their satura- tion magnetization value by assuming Co 4+ in intermedi- ate spin state and that would lead to the same magnetic moment we obtained. code. 0 and i stand for central atom and coordination shell index, respectively. The detailed electronic and magnetic properties of a single-layered compound - Sr$_{2}$CoO$_{4}$ - have been studied using ab initio calculations with different formulations of the density functional theory. The GGA calculation gives a ferromagnetic metallic state with total magnetic mo- ment of ∼ 2 µ$_{B}$ /fu. The GGA+ U calculations provide two ferromagnetic solutions with S = 3/2 spin config- uration: (i) half-metallic and (ii) metallic. The ferro- magnetic half-metallic state is the lowest energy state and representative of the ground state. Our results also suggest that the compound may show metal to insulator transition when a small amount hole is doped at the Co sites. In the present work we have also estimated the crystal-field energy, magnetic moments, Heisenberg ex- change parameters, transition temperature, etc ., which provide good description of experimentally observed elec- tronic and magnetic properties of the system. Finally, we discuss the physical implications of our re- sults. The half-metallic ferromagnet has potential appli- cation in the sprintonics industry. 26 This compound can be considered as a good candidate as it shows T$_{C}$ closer to the room temperature. The d PDOS at the E$_{F}$ are quite low (0.19 states/eV/atom) as evident from the S1 of Fig. 4. This suggests that even a moderate hole dop- ing at the Co sites can lead to insulating ground state. The present work predicts the saturation magnetization of ∼ 3 µ$_{B}$ /fu. The 5K M(H) data of Wang et al . do not show any sign of saturation at maximum measured field of 5 T where the value of magnetization is found to be about 1.4 µ$_{B}$ /Co. 4 However, their M(T) data suggest to support our calculated S = 3/2 spin state as they have reported the effective magnetic moment of ∼ 3.72 µ$_{B}$ . Here it is important to note that M(H) data of Matsuno et al . show almost saturation of magnetization at 7 T where the value of magnetization is found to be about 1.8 µ$_{B}$ /Co. 3 However, this work has been carried out on the thin films, which may suffer from the effects of sub- strate induced strain and/or defects present in the films. IV. CONCLUSIONS Nearest neighbour Coordination number J$_{0}$$_{i}$ (meV) 1 st 4 19.06 2 nd 4 -1.11 3 rd 8 1.25 4 th 4 -0.33 6 ∗ Electronic mail: sk$_{−}$iuc@rediffmail.com 1 M. Imada, A. Fujimori, and Y. Tokura, Rev. Mod. Phys. 70 , 1039 (1998). 12 V. I. Anisimov, F. Aryasetiawan, and A. I. Lichtenstein, J. 11 J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77 , 3865 (1996). 10 S. H. Vosko, L. Wilk, and M. Nusair, Can. J. Phys. 58 , 1200 (1980). 9 S. Y. Savrasov, Phys. Rev. B 54 , 16470 (1996); Z. Kristal- logr. 220 , 555 (2005). 8 S. Huang, K. Ruan, Z. Lv, L. Zhuang, P. Wei, H. Wu, M. Li, J. Zhang, Y. Chai, H. Yang, L. Cao, and X. Li, Phys. Rev. B 73 , 094431 (2006). 7 R. Ang, Y. P. Sun, X. Luo, C. Y. Hao, X. B. Zhu, and W. H. Song, Appl. Phys. Lett. 92 , 162508 (2008). 6 Y. Shimada, S. Miyasaka, R. Kumai, and Y. Tokura, Phys. Rev. B 73 , 134424 (2006). 5 K. -W. Lee and W. E. Pickett, Phys. Rev. B 73 , 174428 (2006). 4 X. L. Wang and E. Takayama-Muromachi, Phys. Rev. B 72 , 064401 (2005). 3 J. Matsuno, Y. Okimoto, Z. Fang, X. Z. Yu, Y. Matsui, N. Nagaosa, M. Kawasaki, and Y. Tokura, Phys. Rev. Lett. 93 , 167202 (2004). 2 Y. Maeno, H. Hashimoto, K. Yoshida, S. Nishizaki, T. Fu- jita, J. G. Bednorz, and F. Lichtenberg, Nature 372 , 532 (1994). 24 A. I. Liechtenstein, M. I. Katsnelson, V. P. Antropov, and 23 A. I. Liechtenstein, M. I. Katsnelson, and V. A. Gubanov, Solid State Commun. 54 , 327 (1985). 22 www.flapw.de 21 H. Wu, T. Burnus, Z. Hu, C. Martin, A. Maignan, J. C. Cezar, A. Tanaka, N. B. Brookes, D. I. Khomskii, and L. H. Tjeng, Phys. Rev. Lett. 102 , 026404 (2009). 20 H. Wu, M. W. Haverkort, Z. Hu, D. I. Khomskii, and L. H. Tjeng, Phys. Rev. Lett. 95 , 186401 (2005). 19 S. K. Pandey, S. Patil, V. R. R. Medicherla, R. S. Singh, and K. Maiti, Phys. Rev. B 77 , 115137 (2008). 18 S. K. Pandey, A. Kumar, S. Banik, A. K. Shukla, S. R. Barman, and A. V. Pimpale, Phys. Rev. B 77 , 113104 (2008). 17 B. Dorado, B. Amadon, M. Freyss, and M. Bertolus, Phys. Rev. B 79 , 235125 (2009). 16 K. Kn ´ i zek, Z. Jir´ a k, J. Hejtm´ a nek, and P. Nov´ a k, J. Phys.: Condens. Matter 18 , 3285 (2006). 15 M. A. Korotin, S. Y. Ezhov, I. V. Solovyev, V. I. Anisimov, D. I. Khomskii, and G. A. Sawatzky, Phys. Rev. B 54 , 5309 (1996). 14 K. P. Ong, P. Blaha, and P. Wu, Phys. Rev. B 77 , 073102 (2008) 13 S. K. Pandey, A. Kumar, S. Patil, V. R. R. Medicherla, R. S. Singh, K. Maiti, D. Prabhakaran, A. T. Boothroyd, and A. V. Pimpale, Phys. Rev. B 77 , 045123 (2008). Phys.: Condens. Matter 9 , 767 (1997).