Element-specific electronic structure of Mn dopants and ferromagnetism of (Zn,Mn)O thin films J. Jin a , G.S. Chang b , D.W. Boukhvalov c,d , X.Y. Zhang a, ⁎, L.D. Finkelstein c , W. Xu a , Y.X. Zhou a , E.Z. Kurmaev c , A. Moewes b a Department of Physics, Surface Physics Laboratory (National Key Laboratory) and Synchrotron Radiation Research Center of Fudan University, 220 Handan Road, Shanghai 200433, China b Department of Physics and Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon, SK, Canada S7N 5E2 c Institute of Metal Physics, Russian Academy of Sciences-Ural Division, Yekaterinburg 620219, Russia d Institute for Molecules and Materials, Radboud University, 6525 ED Nijmegen, The Netherlands abstract article info Article history: Received 27 February 2009 Received in revised form 5 November 2009 Accepted 19 December 2009 Available online 4 January 2010 Keywords: Soft X-ray spectroscopy Electronic structure Ferromagnetism (Zn,Mn)O Element-specific electronic structure of (Zn,Mn)O thin films with various Mn concentrations has been investigated using X-ray absorption and emission spectroscopy. According to comparison between the experimental spectra and the density functional theory calculations (partial density of states and exchange interactions for various Mn defect configurations), the substitutional Mn impurities do not induce ferromagnetism in (Zn,Mn)O samples. The ferromagnetic properties can be obtained when defect configurations consisting of both substitutional and interstitial Mn atoms are present. The ferromagnetism in ZnO-based magnetic semiconductors is favored to be Ruderman–Kittel–Kasuya–Yoshida type and the established theoretical model is in a good agreement with the X-ray spectroscopic measurements. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Transition metal-doped semiconductors, called diluted magnetic semiconductors (DMSs) have attracted great attention in recent years since they are being considered as key components for spintronic applications [1–3]. Among promising candidates, Mn-doped ZnO has been studied extensively, which was motivated by the theoretical prediction of ferromagnetism in this system at room temperature (RT) [4]. Ferromagnetic (FM) behaviors of (Zn,Mn)O systems have been experimentally observed both at low temperature (∼ 45 K) and RT [5–10], although ferromagnetism has not been established in poly- crystalline samples prepared under thermal equilibrium condi- tions [11]. Meanwhile, the controversy has swelled around the issue whether ferromagnetism in the ZnO-based DMS materials is carrier-induced (intrinsic) or due to the formation of Mn-related secondary phases (extrinsic). Several mechanisms such as the Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction [12], the double exchange interaction [13], and the Zener model [4] have been proposed to shed light on the origin of ferromagnetism. However, the situation became even more complicated when paramagnetic or antiferromagnetic (AFM) behaviors were also observed in (Zn,Mn)O materials [14,15]. That is why it is highly desirable to understand the origin of various forms of magnetism in (Zn,Mn)O. Since the magnetic properties of (Zn,Mn)O systems are known to strongly correlate with an exchange interaction between magnetic impurity atoms, an approach to study the local electronic structure near them in detail is promising. In the present study, we performed ab initio calculations of electronic structure and exchange interactions in (Zn,Mn)O system based on different defect configurations and compared our results to soft X-ray absorption/emission spectroscopy measurements. Our results suggest that the ferromagnetism results from interstitial Mn atoms interacting with the adjacent substitutional Mn atoms. A RKKY- type exchange interaction is directly observed in our samples. 2. Experimental details The Zn 1 - x Mn x O thin films with various Mn concentrations (x =0.03, 0.06, 0.11, 0.20, and 0.33) were grown by a molecular beam epitaxy on Si (100) substrate with a ZnO buffer layer. The substrate temperature and oxygen partial pressure were kept constant at 200 °C and 1.06×10 -3 Pa, respectively. According to vibrating sample mag- netometry measurements, the Zn 1 -x Mn x O samples with low Mn concentration (x =0.03, 0.06, and 0.11) exhibit FM behaviors while the AFM coupling is observed for the samples with 20 and 33% of Mn concentration. The Curie temperature (T C ) of Zn 1 -x Mn x O with x = 0.03 is about 45 K. The AFM behaviors of the heavy-doped samples are attributed to a formation of MnO secondary phase as confirmed by X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) Thin Solid Films 518 (2010) 2825–2829 ⁎ Corresponding author. Tel.: +86 21 65643522; fax: +86 21 65643626. E-mail address: xy-zhang@fudan.edu.cn (X.Y. Zhang). 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2009.12.100 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf