Journal of Alloys and Compounds 477 (2009) 379–385 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Room temperature ferromagnetism in Mn-doped dilute ZnO semiconductor: An electronic structure study using X-ray photoemission R.K. Singhal a,∗ , M.S. Dhawan a , S.K. Gaur a , S.N. Dolia a , Sudhish Kumar b , T. Shripathi c , U.P. Deshpande c , Y.T. Xing d , Elisa Saitovitch d , K.B. Garg a a Department of Physics, University of Rajasthan, Jaipur 302004, India b Department of Physics, ML Sukhadia University, Udaipur 313002, India c UGC-DAE CSR, University Campus, Indore 452001, India d CBPF, Rua Xavier Siguad 150, Urca, Rio de Janeiro, RJ, Brazil article info Article history: Received 22 April 2008 Received in revised form 25 September 2008 Accepted 2 October 2008 Available online 21 November 2008 Keywords: Magnetically ordered materials Solid state reaction Magnetization X-ray diffraction X-ray photoelectron spectroscopy abstract There are several confronting reports of room temperature ferromagnetic (FM) ordering in bulk as well as thin films of dilutely doped or even some undoped semiconductors. We have synthesized and charac- terized dilute Mn-doped (2 and 4%) ZnO pellets. SQUID measurements confirm that the 2% Mn sample shows the FM ordering above the room temperature and the FM contribution coming mainly from the bulk. However, the ordering gets completely quenched for 4% Mn doping. Upon cooling down, the 2% Mn-doped sample shows further enhancement in the magnetic properties while the 4% sample did not show any FM ordering down to 5 K. The powerful X-ray photoemission spectroscopy (XPS) was employed to compare the electronic structure of these two samples. The XPS results show that the manganese shifts toward the higher valence state upon Mn doping while there is no change in the zinc and oxygen valence. The atomic concentration of divalent Mn state is found to be dominant in the ferromagnetic sample. For the non-ferromagnetic sample, a larger contribution of higher oxidation Mn states is present that is cor- related to the suppressed ferromagnetism. Interestingly, the oxygen content is also found to be higher in the 4% Mn sample than that in the 2% Mn sample that has been attributed to the charge neutrality of the samples. The present study provides evidence that the magnetization originates neither from any precipitating secondary phase nor from the oxygen content but the Mn 2+ state plays a significant role for the FM properties in the Mn-doped ZnO system. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Dietl et al. [1] theoretically predicted that the ferromagnetism at high temperature can be obtained in many wide band gap semicon- ductors such as ZnO, GaAs, GaN, etc. if we dope Mn plus a certain concentration of holes into these systems, basically as p-type. The magnetic ordering was supposed to be originated from the RKKY interaction via the dopants. Following this prediction, experimen- talists have tried intensively [2–11] over the past few years to dope transition-metals (TM) into many semiconducting oxides such as ZnO, TiO 2 , SnO 2 , In 2 O 3 and actually the room temperature ferro- magnetism was observed in these. However, the phenomenon is not exactly as what Dietl predicted, because in most of the cases, the compounds are found to be n-type. The research in this field has been fuelled by the possibility of exploiting their spin-transport ∗ Corresponding author. Tel.: +91 141 2545931; fax: +91 141 2701038. E-mail address: singhal46@yahoo.co.in (R.K. Singhal). properties in making spintronic devices where the ferromagnetism is combined to their semiconducting, optical and piezoelectric properties. The cause of origin of ferromagnetism in these diluted magnetic semiconductors (DMS) such as transition-metal-doped ZnO has long been debated, but it is yet to be resolved due to a lot of controversies [12–18]. The first reports of room temperature FM ordering in Mn-doped ZnO powder, bulk pellets as well as 2–3 m laser-ablated trans- parent films with Curie temperatures far above 425 K came from Sharma et al. [19,20]. This was subsequently confirmed by Blythe et al. [21] in their mechanically alloyed samples who made a detailed study of dependence of the FM ordering on the processing tem- perature. Lin et al. [13] also reported ferromagnetism in Zn 1-x Fe x O compounds, fabricated by mechanical alloying, with the Curie tem- perature higher than room temperature and concluded that Fe atoms dissolve in the ZnO lattice in Fe 2+ and Fe 3+ state. However, Kane et al. [22] claimed no evidence of diluted magnetic semicon- ductor mean-field FM behaviour in Zn 1-x Mn x O, Zn 1-x Co x O bulk single crystals. Instead, they report a paramagnetic behaviour in 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.10.005