Contents lists available at ScienceDirect Materials Science & Engineering B journal homepage: www.elsevier.com/locate/mseb Spin effect on electronic, magnetic and optical properties of spinel CoFe 2 O 4 : A DFT study A. Hossain, M.S.I. Sarker ⁎ , M.K.R. Khan, M.M. Rahman Department of Physics, University of Rajshahi, Rajshahi 6205, Bangladesh ARTICLE INFO Keywords: Spin polarization Magnetic moments Elastic constants Optical properties Surface plasmon resonance ABSTRACT This report demonstrates the structural, electronic, magnetic, elastic, and optical properties of spinel CoFe 2 O 4 using generalized gradient approximation (GGA). Both the spin and non-spin polarized density functional theory (DFT) have been used to study the influence of spin interactions on electronic structures, spin magnetic mo- ments, and optical properties. The calculated magnetic moments of CoFe 2 O 4 from spin density of states are 6.98 μ B per formula unit. The Fe and Co ions prefer high spin orientations owing to the cationic polarization because of crystal field strength and intra-atomic exchange interactions, which induces large spin magnetic moments. The high values of spin magnetic moments confirm strong spin orbit coupling due to strong electron-electron interactions and can be a promising for spintronic application. Moreover, the calculated high reflectivity of CoFe 2 O 4 material (~100%) in the Infrared-Visible-Ultraviolet region up to ~30 eV, which suggesting that the CoFe 2 O 4 can also be a good candidate for solar reflector. 1. Introduction The spinel compounds of AB 2 O 4 family (such as NiFe 2 O 4 , MgFe 2 O 4 and CoFe 2 O 4 etc.) are very important in materials science and en- gineering due to their wide range of aptness and outstanding properties. In stoichiometric formula of AB 2 O 4 structure A, B and O are the divalent cations, trivalent cations and divalent anions, respectively. For inverse spinel oxide, A atom shared by octahedral sites and B atom shared evenly by both tetrahedral and octahedral sites. Spinel ferrites have great attraction due to its rich magnetic and electronic properties. Particularly, the spinel CoFe 2 O 4 has great im- portance due to its unique physical and chemical properties. It exhibits high Curie temperature, low coercivity, moderate saturation magneti- zation, high magnetic moment, large magneto crystalline anisotropy, high magnetostrictive coefficient, excellent chemical stability, and mechanical hardness [1–8]. These properties assign CoFe 2 O 4 as a technologically important and suitable for high density magnetic re- cording media [9], ferro-fluid applications, biomedicine, magnetic re- sonance imaging, biosensors, magnetic hyperthermia-based therapy [10], data storage, magnetic refrigerators and microwave devices [11]. The arrangement of divalent and trivalent cations in tetrahedral and octahedral voids plays a crucial role on its electronic structures as well as on physical properties of spinels. The cation distribution of CoFe 2 O 4 can be expressed as: − − Co Fe Co Fe ( ) [ ] x x Td x xO 1 2 h , where, x is the degree of inversion parameter. For normal spinels (x = 0), the tetrahedral (T d ) and octahedral (O h ) sites are occupied by Co 2+ and Fe 3+ cations, re- spectively, while in the inverse spinels (x = 1) all the Co 2+ cations occupy the octahedral sites and Fe 3+ cations occupy both tetrahedral and octahedral sites. Combining a divalent cation with an inversion degree offers a huge variety of structural, electronic, and magnetic properties of spinel ferrites [12]. The magnetic properties of spinel cobalt ferrites are contributed by the super-exchange interaction be- tween the metal ions located at the tetrahedral and octahedral sites [13]. Moreover, spinel CoFe 2 O 4 demonstrated ferrimagnetic ground state with high spin orientations on tetrahedral to octahedral sites [14,15]. Experimental studies so far dealt with structural, magnetic and electrical properties of CoFe 2 O 4 [4,16–20]. Many theoretical studies have been performed on inverse and normal spinel of CoFe 2 O 4 using DFT theory through various approx- imations such as local spin density approximation (LSDA) [21,22], Generalized Gradient approximations (GGA) or by introducing on-site Coulomb repulsion energy (U) through the LSDA + U [23] and GGA + U approaches [24] or even by using the self-interaction cor- rected (SIC)-LSDA method [25]. The LSDA and GGA approaches gen- erally describe these materials to be half-metallic or metallic, if no distortions are included. The SIC-LSDA method, which is parameter free, may provide a better description of correlations than LSDA, but requires a much heavier computing resource than LDA or GGA. All the https://doi.org/10.1016/j.mseb.2020.114496 Received 23 May 2018; Received in revised form 3 October 2019; Accepted 8 January 2020 ⁎ Corresponding author. E-mail address: samiul-phy@ru.ac.bd (M.S.I. Sarker). Materials Science & Engineering B 253 (2020) 114496 0921-5107/ © 2020 Elsevier B.V. All rights reserved. T