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In the present study, nanocrystalline undoped and Fe (5 wt.%) doped ZnO powder has been synthesized by soft chemical route. The structural, nano/microstructural, vibrational and magnetic properties of these samples have been studied as a function of calcination temperature (400°C to 1100°C). X-ray diffraction analysis of Fe doped ZnO powder has shown the major nanocrystalline wurtzite (ZnO) phase and the minor cubic spinel-like secondary nanocrystalline phase at 700°C. At calcination temperature of 700°C, the magnetization and coercivity have been enhanced in Fe doped ZnO. As the calcination temperature increased to 1100°C, the major phase of ZnO and minor cubic spinel-like secondary phase turned into bulk in doped ZnO. Interestingly, the reduced magnetization and zero coercivity have been observed in this case. These changes are attributed to the conversion of secondary nanocrystalline ferromagnetic spinel phase to its bulk paramagnetic phase. The degree of inversion i.e. the occupancy of both sites with different symmetry by ferric ions is proposed to be solely responsible for the unusual behavior. Keywords: ZnO nanocrystal; Fe doped ZnO nanocrystal; sol-gel route; X-ray diffraction; secondary phase; room temperature ferromagnetism Room temperature ferromagnetic behavior in the nanocrystals of Fe doped ZnO synthesized. . .

Nanocrystalline undoped and 5% Mn doped ZnO powders are synthesized by sol-gel route using constituent nitrate and citrate precursors. The physico-chemical characterizations of powders calcined at various temperatures (400-1100 ˚C), are performed using techniques (XRD and SQUID) to study structural, nano/microstructural, and magnetic properties. XRD patterns clearly revealed the evolution of major wurtzite (ZnO) and minor non-stoichiometric defect cubic spinel phase of ZnMnO 3- . Unexpectedly, the magnetic hysteresis loop with its large magnetic parameters are observed at room temperature as soon as the concentration of the minor phase is large enough. The analysis of the unusual room temperature ferromagnetic behavior is presented in this communication based on the dominant contributions of the secondary nanocrystalline non-stoichiometric defect cubic spinel phase of ZnMnO 3- .KEYWORDS: Diluted magnetic semiconductor, soft chemical route, Mn doped ZnO, Room temperature ferromagnetism I. INTRODUCTION In the recent past, a surge of interest is observed in the studies of diluted magnetic semiconductor (DMS) oxides due to simultaneous utilization of charge and spin of electrons in a single material to develop new functionalities [1][2][3][4]. These DMSs are potential candidates for technological application such as spintronic devices. Recently, this class of materials is studied extensively for better understanding of basic mechanisms of different types of magnetic interactions in diluted system. Among these materials, we focused our attention on undoped and doped ZnO based DMS. Dietl et al reported room temperature ferromagnetic (RTFM) behavior arising from carrier mediated exchange interaction has been predicted for several transition metal (Mn, Fe, Co, etc) doped ZnO and GaN DMSs. [2]. The large amount of experimental work on Mn doped ZnO based DMSs has been reported in literature with contradictory experimental results in favor of RTFM [5][6][7] when processed at lower temperature and against of RTFM [8,9] when processed at higher temperature. Similar results are obtained in different product (bulk and nanoparticles) forms prepared by different synthesis along with different processing parameters [5][6][7][8][9]. In spite of the tremendous amount of experimental work, the origin of RTFM behavior and the associated energy exchange interactions are not fully understood. In the present investigation, the RTFM behavior of sol-gel synthesized nanoparticles of 5% Mn doped ZnO is discussed in terms of secondary nanocrystalline defect cubic spinel (DCS) phase of ZnMnO 3- .

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