DC Electrical Resistivity and Magnetic Property of Single-Phase a-Fe 2 O 3 Nanopowder Synthesized by a Simple Chemical Method Prita Pant Sarangi, z Sampat Raj Vadera, y Manoj Kumar Patra, y Chandra Prakash, z and Narendra Nath Ghosh w,z z Chemistry Group, Birla Institute of Technology and Science—Pilani, Goa Campus, Zuarinagar 403726, India y Defence Lab, Rajasthan, Jodhpur 342011, India z Directorate of ER&IPR, DRDO, DRDO Bhawan, New Delhi 110105, India Nanocrystalline pure a-Fe 2 O 3 powder, with an average particle size of 35 nm, has been synthesized by using an aqueous solution- based synthetic route. DC electrical resistivity of the synthesized material was measured with respect to temperature by the two- probe method from 281 to 2251C. Room temperature resistivity of the nanopowder was B10 8 X . cm. Magnetic hysteresis mea- surement revealed that the synthesized a-Fe 2 O 3 nanopowder exhibited ferromagnetic behavior at room temperature. The hysteretic features are high saturation magnetization of 5.1 emu/g, high remanence of 2.2 emu/g, and coercivity of 200.5 Oe. I. Introduction N ANOSTRUCTURED iron oxide has myriad applications in di- verse fields. Its application can be put to use in high-den- sity magnetic recording media, as contrast agents in magnetic resonance imaging (MRI), as superparamagnetic (SPM) nano- particles in biomedicines, clinical diagnosis, and treatment, as sensors, and in catalysis, 1,2 etc. The influence of the nanostruc- ture of iron oxides on their electric and magnetic properties has gained immense interest in recent years. This has led towards the development of various synthesis routes for the preparation of iron oxides with different crystalline phases and microstruc- tures. Laurent et al. 3 and Pant et al. 4 have reviewed different synthetic methods used for the preparation of magnetic iron oxide and ferrite nanoparticles, respectively. Bulk hematite is canted antiferromagnetic at room tempera- ture and undergoes a Morin transition at B263 K. 5 Iron oxide nanoparticles exhibit different magnetic properties compared with bulk iron oxide, such as high coercivity, 6 suppression of the Morin transition, 6 enhancement of susceptibility, 7 and su- perparamagnetism, 7,8 etc. Important factors that contribute to the unique magnetic properties of a-Fe 2 O 3 nanoparticles are (i) a large surface-to-volume ratio of the nanoparticle, (ii) site-specific surface anisotropy, 9 (iii) exchange anisotropy, 9 (iv) shape anisot- ropy for nonspherical particles, 10 (v) interparticle exchange in- teractions, 11 etc. Polycrystalline bulk hematite, with nearly complete densifi- cation, exhibits a room temperature resistivity of B10 14 O Á cm 12 . The electrical resistivity of hematite nanopowders is determined by several important factors such as morphology, porosity, and humidity, 13–15 etc. Therefore, it is crucial to in- vestigate the effect of microstructure on the electrical resistivity of a-Fe 2 O 3 nanopowder. We have developed a novel aqueous solution-based chemical method for the preparation of a pure a-Fe 2 O 3 nanopowder. 16,17 In this communication, we have reported the electrical and magnetic properties of the synthesized a-Fe 2 O 3 nanopowders prepared by this method. We have investigated the change of DC electrical resistivity of the synthesized material with the change of temperature and microstructure. The synthesized a- Fe 2 O 3 nanopowder exhibits a high room temperature resistivity of B10 8 O Á cm. Room temperature VSM measurement revealed that the material possesses a high saturation magnetization (M S ) of 5.1 emu/g at 0.2 T and a remanence magnetization of 2.2 emu/g at a zero field. II. Experimental Procedure (1) Synthesis of a-Fe 2 O 3 Nanopowder In a typical synthesis, an aqueous solution of 0.1 mol ferric ni- trate nonahydrate (99.9%, Merck, Mumbai, India) in 150 mL of distilled water was mixed with 100 mL of an aqueous solution of 0.1 mol EDTA (99.9%, Merck) and stirred for 1 h at room temperature using a magnetic stirrer. A dark brown fluffy pow- der (precursor) was formed when this mixture was evaporated to dryness on a hot plate at B1251C. Calcination of the precursor powder in air for 2.30 h at 4501C resulted in the formation of a a-Fe 2 O 3 nanopowder. 16 X-Ray Diffraction (XRD) spectra of the precursor and calci- ned powders were recorded using a Rigaku powder X-ray diffractometer (Mini Flex II, Japan) with CuKa radiation. The- rmogravimetric analysis (TGA) and differential scanning calori- metric (DSC) analysis were carried out for the precursor using a Shimadzu DTG–60 (Japan) and Shimadzu DSC–60, respectively, in air at a heating rate of 201C/min from 401 to 5501C. The mor- phology of the samples was studied using JEOL scanning electron microscopy (SEM) (JSM 6360LV, Japan) at an accelerating volt- age of 20kV. The particle size of the synthesized powder was de- termined by using a FEI HRTEM (Tecnai G2 30 S-Twin, FEI, Eindhoven, the Netherlands) at an accelerating voltage of 300kV. DC electrical resistivity was measured from room temperature (281) to 2251C by the two-probe method using a Keithley Elect- rometer (6517 A, Keithley Co. Ltd., Cleveland, OH). Room tem- perature magnetization was measured with respect to the external magnetic field by using an ADE vibrating sample magnetometer (VSM) EV5. III. Results and Discussion Thermal analysis (TGA-DSC) of the precursor showed that its oxidative decomposition to Fe 2 O 3 occurred in two major weight B. van Dover—contributing editor This work was financially supported by DRDO (EPIR/ER/060/5042/M/01/929). w Author to whom correspondence should be addressed. e-mail: naren70@yahoo.com Manuscript No. 26110. Received April 3, 2009; approved May 14, 2009. J ournal J. Am. Ceram. Soc., 92 [10] 2425–2428 (2009) DOI: 10.1111/j.1551-2916.2009.03213.x r 2009 The American Ceramic Society 2425