Structural, electronic and magnetic properties of Ti 1þx FeSb Heusler alloys Said M. Azar a, * , Ahmad A. Mousa b , Jamil M. Khalifeh c a Department of Basic Sciences, Dar Al Uloom University, Riyadh, Saudi Arabia b Department of Basic Sciences, Middle East University, Amman,11831, Jordan c Department of Physics, The University of Jordan, Amman, 11942, Jordan article info Article history: Received 31 May 2016 Received in revised form 6 January 2017 Accepted 17 February 2017 Available online 6 March 2017 Keywords: Heusler alloys Half-metal First principles DFT FP-LAPW TB-mBJ abstract Density functional theory calculations based on full potential linearized augmented plane-wave (FP- LAPW) plus local orbital method in the framework of GGA-PBE, as embodied in the WIEN2k code, is used to investigate the structural, electronic and magnetic properties of intermetallic Ti 1þx FeSb Heusler compounds, where (x ¼0:75; 0:50; 0:25; 0:0; 0:25; 0:50; 0:75; 1:0). Moreover, the Tran-Blaha parameterized of the modified Becke-Johnson (TB-mBJ) exchange potential, as a semi-local method, is employed to predict the bandgap more precisely. The physical characteristic of these systems are found to be mostly determined by the crystal structure and the electron concentration or the number of valence electrons. We examined the site preference of the parent compound TiFeSb and varied the electron concentration by doping or removing a Ti atom and we found that the variation plays a crucial role in the physical properties of these material systems. Alloys with x  0 are found to exhibit a ferrimagnetic phase, and the alloy with x ¼ 0:25 exhibits non-magnetic properties, whereas the rest have shown ferromagnetic phase. The band-structure analysis of Ti 1:75 FeSb and Ti 2 FeSb (CuHg 2 Ti-type) alloys sug- gested that they could be ferromagnetic half-metallic candidates with bandgaps 0.350 and 0.468 eV, respectively. We found that Ti rich Ti 1þx FeSb alloys have high spin polarization. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The half-metallicity was first predicted in 1983 by de Groot et al: for the half-Heusler alloy NiMnSb [1] and Kücbler first realized their high magnetic moments and high spin polarization [2]. Heusler phases (X 2 YZ and XYZ) are considered to be most attractive can- didates for application in spintronic devices, since they exhibit extremely high Curie temperatures (905 K for Co 2 MnGe), low co- ercivities and good lattice matching with conventional semi- conductors such as GaAs. Used in MTJs with MgO tunnel barriers, TMR values as high as 750% at 2 K have been reached [3]. Ternary transition metal antimonid systems have recently attained more interest because of their possibility in technological applications such as spintronic as well as thermoelectric power generation. In addition, the lack of complete knowledge on phase formation and equilibria, crystal structure and homogeneity range as well as the diversity of the physical properties such as magnetic order, semiconducting-like behavior, half-metallicity and large Seebeck coefficient versus composition motivated the authors to investigate these systems. FeTiSb and other intermetallic semi- Heusler compounds and their solid solutions were investigated experimentally and theoretically. Their physical properties are influenced by the number of valence electrons. Some discrepancy was found between experimental and theoretical results [4]. In TiFeSb case, the compound is close to the magnetic-nonmagnetic boundary and its properties are very sensitive to any kind of atomic disorder [5]. Szytula et al:, by extensive experimental studies of FeTiSb alloy observed a Curie-Weiss like paramagnetism phase, with paramagnetic moment close to 2.8 m B , and its crystal- lographic structure is more complex than the normal semi-Huesler [6]. Experimental and theoretical study of the structural and transport properties of quaternary half-Heusler Fe 1x Ni x TiSb alloys employed X-ray diffraction, 57 Fe M€ ossbauer spectroscopy, re- sistivity, thermopower measurements, and KKR-CPA method. The presence of the energy gap at the nine bands allows us to consider FeTiSb compound as one hole system. Conversely, the KKR-CPA on a disordered ðTi 0:5 E 0:5 Þ 2 FeSb (E denotes vacant site), in which Ti atoms are distributed randomly on two equivalent sites in the * Corresponding author. E-mail address: said@dau.edu.sa (S.M. Azar). Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet http://dx.doi.org/10.1016/j.intermet.2017.02.018 0966-9795/© 2017 Elsevier Ltd. All rights reserved. Intermetallics 85 (2017) 197e205