Journal of Alloys and Compounds 508 (2010) 419–425 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Investigations of DC-magnetization behavior of nanocrystalline ZnO:Ni Vidhi Goyal a , Kanwal Preet Bhatti b,∗ , Sujeet Chaudhary a a Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India b Department of Physics, Guru Nanak Dev University, Amritsar 143005, India article info Article history: Received 1 June 2010 Received in revised form 13 August 2010 Accepted 24 August 2010 PACS: 75.50.Pp 75.50.Dd 75.60.Ej Keywords: Magnetically ordered materials Oxide materials Magnetic measurements abstract Ferromagnetic character observed in chemically synthesized nanocrystalline ZnO:Ni (upto 10 at% Ni) powder samples has been tracked vis-à-vis the processing conditions. The DC-magnetization behavior is found to be strongly dependent upon the employed sample processing conditions. While the as-calcined samples are strongly ferromagnetic due to the presence of nickel clusters; sintering of the samples to higher temperature in air ambient oxidizes Ni clusters and the magnetic behavior of the samples undergo significant changes. The samples are no longer completely ferromagnetic and are a mixture of ferro- magnetic, antiferromagnetic, paramagnetic and diamagnetic fractions, depending upon the temperature dependent solubility limit of Ni in ZnO. This work further clearly suggests that the weak room temper- ature ferromagnetism observed in the ZnO:Ni samples (upto 10 at% Ni), sintered in air at 900 ◦ C/12 h, is an intrinsic effect. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Ferromagnetic semiconductors (FMSs) are one of the promising materials in the emerging field of spintronics. For realizing practical devices, a key requirement is that the host material should be fer- romagnetic at or above room temperature. Due to the outstanding optical and electrical properties, considerable attention has been focused on ZnO-based FMSs in the past few years. Magnetic charac- teristics and possible mechanisms have been studied theoretically [1,2] and experimentally in ZnO doped with transition metals [3–12]. Ferromagnetism with a Curie temperature (T C ) higher than room temperature has been reported in many cases in Co doped ZnO [3,4]. In the case of Ni doped ZnO, relatively fewer studies have been reported since its preparation is particularly challenging due to the large driving force for phase segregation into NiO and ZnO. In the case of Ni doped ZnO, thin films prepared by spin coat- ing [5], direct current magnetron cosputtering [6,7], pulsed laser deposition [8–10], sol–gel [11], rf magnetron sputtering [13,14] and electrochemical means [15] have been studied. In some cases, nickel doped ZnO nanocrystals [16] and thin films [13] are found to be paramagnetic. However, in other cases, nanocrystalline powder samples [17–19] and nanorods [20] are reported to be ferromag- netic or even superparamagnetic [21]. Large variations in magnetic ∗ Corresponding author. Fax: +91 183 2258819. E-mail address: kanwalbhatti@gmail.com (K.P. Bhatti). properties for Ni doped ZnO indicate that ferromagnetism in this system strongly depends on the methods and conditions used in their preparation. Moreover, even the conclusion of intrinsic fer- romagnetism remains controversial. In some cases, the observed room temperature ferromagnetism (RTFM) was claimed to be car- rier mediated [19,23] or occurring due to defects [22] or oxygen vacancies [24–26]. Still in a few other cases, Ni clusters were responsible for observed RTFM [27–29]. It is also reported that homogeneous incorporation of Ni in ZnO results in paramagnetic samples, whereas the imperfectly doped samples lead to ferromag- netism [30]. In case of ZnO samples codoped with Li and Ni, it is observed that the insulating films are superparamagnetic, whereas the n and p type films exhibit RTFM [25]. Therefore, detailed study of the influence of doping concentration on ferromagnetism is par- ticularly necessary and effective for understanding the intrinsic origin of ferromagnetism. In the present work, we report the results of detailed investi- gation and the possible origin of the observed magnetic behavior in chemically synthesized nanocrystalline Zn 1-x Ni x O powder sam- ples. The results of the effect of processing parameters on the magnetization (M), structural and phase purity of the nickel sub- stituted ZnO nanocrystalline powder samples are presented in this paper. 2. Experimental The chemical method for the synthesis of oxide particles was chosen as it results in better homogeneity and the obtained powders have smaller grain size as com- 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.08.078