Defect dependent polarized spin current in 1% Co doped ZnO thin films Musa Mutlu Can a,b,n , S. Ismat Shah c,d , Tezer Firat e a Department of Physics, Faculty of Science, İstanbul University, 34314, Vezneciler, İstanbul, Turkey b CNR-SPIN, Universitá di Napoli “Federico II”, Compl. Univ. di Monte S. Angelo, Via Cintia, I-80126, Napoli, Italy c Department of Physics and Astronomy, University of Delaware, 19716, Newark, DE, USA d Department of Material Science and Engineering, University of Delaware, 19716, Newark, DE, USA e Department of Physics Engineering, Hacettepe University, TR-06590 Ankara, Turkey article info Article history: Received 23 April 2014 Available online 28 October 2014 Keywords: ZnO-related semiconductor Diluted magnetic semiconductor (DMS) Polarized spin current Anomalous Hall effect abstract The magnetic nature in Co and W doped ZnO lattice, which included specific concentration of defects, is investigated by magneto electrical measurements. The results are reported based upon the findings of longitudinal and transverse magneto electrical transport changes at 2 K. The transverse magneto elec- trical transport analyses are carried out with the scanning speeds of 20 Oe/s, 50 Oe/s, 100 Oe/s and 190 Oe/s in order to understand the relaxation of polarized spins. In the highest scan speed of 190 Oe/s, the relation between the polarized spins and positive magneto resistivity is revealed through both hole and electron mediated interactions. Although Hall resistance measurements show the dominant carriers as n-type, the 10 71% positive magneto resistivity and a split of about 3.1 70.2 Ohm in magneto hys- teresis curve prove that a polarized spin current is formed under both s–d and p–d interactions effec- tively. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Ferromagnetism in polarized spins in dilute magnetic semi- conductors (DMSs) is based on theories which identify strong exchange coupling between 2p levels of oxygen and d shells of transition metals [1–3], transitions between different valance states of transition metal atoms [2], shallow donors due to s–d interactions with n-type doping [2] and hybridization between the impurity bands of defects and the 3d bands [4], known as d 0 fer- romagnetism. Likewise, the carrier mediated ferromagnetism in the lattice is affected by the types of 3d cations [5], local point defects [6,7], and carrier concentrations [8]. In addition, the tran- sition metals are also used for the n or p type doping and the type of point defects lead to the formation of shallow energy levels [6– 11]. These shallow energy levels are identified as the main para- meter leading to magnetization in dilute magnetic semiconductors (DMSs) [1–7]. This paper describes the results on structural and magneto- electrical analyses of 1% Co doped ZnO thin films. The results identify the polarized spin currents in 1% Co doped ZnO thin films to be due to non-native defects and due to W and Co dopant atoms. The effects of W atoms are already revealed in the previous study [12]; and this study is the further investigation on polarized spin currents in ZnO thin films. In addition to the efficiency of W atoms, we analysed the polarized spin currents in ZnO thin films under condition of substituted 1% (in molar ratio) Co atoms in ZnO thin films. This study experimentally finds the effectiveness of s–d and p–d interactions on the polarized spins and points out results of polarized spin currents in DMSs. 2. Experimental The Co doped ZnO thin films were deposited using a rf mag- netron sputtering system with a 5 cm diameter cathode. A home- made Zn Co O 0.99 0.01 target was used for the thin film deposition. The thin films contain 0.5% tungsten (W) in atomic ratio that originates from the target. The details of target synthesis were reported elsewhere [13]. The deposition was carried out for 60 minutes under 100 W RF (radio frequency) power to the cathode on 10 Â 10 mm 2 Si (100) Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2014.10.080 0304-8853/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: +90 (533) 929 0718; fax: +90 (212) 4555700-15426. E-mail address: musamutlucan@gmail.com (M.M. Can). Journal of Magnetism and Magnetic Materials 377 (2015) 229–238