J Supercond Nov Magn DOI 10.1007/s10948-017-4120-7 ORIGINAL PAPER Electronic and Magnetic Properties of Highly Correlated Half Metallic Layered Sr 2 CoO 4 Cobaltate Using mBJ Exchange Potential Komal Bapna 1 · B. L. Ahuja 1 Received: 18 February 2017 / Accepted: 11 April 2017 © Springer Science+Business Media New York 2017 Abstract We have investigated the electronic and mag- netic response of layered Sr 2 CoO 4 (SCO) using Tran-Blaha modified Becke-Johnson potential (mBJ) within the density functional theory. The optimized lattice parameters were determined for the ground state energy of ferromagnetic SCO. Present calculations reveal a peculiar half metallic character with an indirect band gap of 1 eV in the minor- ity state. The magnetic moments on Co and O atoms are observed to be antialligned with each other, resulting to a magnetic moment of 1 μ B /f.u. Electronic occupancies for the various orbitals of Co and O atoms have been deduced, suggesting the Co-3d xy and O2-p z orbitals to be majorly possessing magnetic moments in the SCO system. Hybridisation between different orbitals and their contri- bution in forming the Fermi surfaces (FSs) are discussed. It is revealed that in half-metallic ferromagnetic SCO, FS structures are formed due to majority spin Co-3d x 2 −y 2 and Co-3d z 2 orbitals hybridised with O-2p orbitals. It is inferred that majority spin Co-3d x 2 −y 2 (dominantly) and p z electrons of O atoms are responsible for the conduction mechanism. Present results provide the usefulness of mBJ approach in deducing the electronic and magnetic proper- ties of layered SCO. Deduction of orbital magnetic moment for cobaltates-like systems would be very crucial to further understand its magnetic properties. Keywords Layered cobaltates · Density functional theory · Magnetic properties  Komal Bapna komal.bapna@gmail.com 1 Department of Physics, M. L. Sukhadia University, Udaipur 313001, India 1 Introduction The two-dimensional (2D) layered cobalt oxides with K 2 NiF 4 -type structure, where the CoO 2 planes are sepa- rated by rock salt-type planes, are quite interesting to study [1, 2]. In these materials, the 2D nature of the CoO 2 net- work induces various fascinating electronic and magnetic properties. Sr 2 CoO 4 (SCO) has a 2D-layered structure with Co in 4+ state. It exhibits ferromagnetism (T C = 255 K) and metallic behaviors, which is unique in such materials [3]. It is reported that the energy difference between Co-3d (t 2g and e g ) levels is rather small and hence, Co 4+ can pos- sess electronic configurations t 4 2g e 1 g , t 5 2g and t 3 2g e 2 g revealing three possible spin states, which correspond to intermedi- ate spin (IS), low spin (LS) and high spin (HS) states. This leads to a peculiar complex ground state magnetic structure. Also, the SCO system shows large magnetic anisotropy and quasi-2D electrical resistivity behaviour, which are quite interesting. Moreover, the compound is predicted to be half-metallic which makes it a potential candidate for the emerging spintronics devices [2–6]. In earlier experimental and theoretical studies on SCO, few authors have reported exotic physical properties and contradicting results on magnetic response [2–6]. Ab initio calculations have been performed with different approaches to study the electronic and magnetic properties of SCO. Lee et al. [5] have reported electronic properties of the system using local density approximation (LDA) + U (where U is on-site Coloumbic repulsion). Pandey [6] has employed generalized gradient approximation (GGA), with and with- out incorporation of U to reveal the ground state properties of the system considering different electronic states of the SCO. The system revealed different values of magnetic moments for different values of U , which leads to contro- versies in the actual magnetic response of SCO. Although,