A simple, mild and environmentally friendly one-pot aqueous synthesis route using urea devoid of surfactant and chelating agents is demonstrated for the first time to fabricate high yield crystalline uniform hexagonal prism-shaped weakly magnetic a-Fe 2 O 3 nanocrystals. As synthesized a-Fe 2 O 3 nanocrystals show ferromagnetic behavior with coercivity values of 0.8 and 0.2 T at 5 and 300 K, respectively. The urea and reaction temperature plays a crucial role, regulating the morphology and the size.Novel high quality magnetic materials of desired size and shape play an important role in modern science and technology. Amongst various nanostructured materials, highly crystalline monodisperse magnetic nanostuructures with various sizes and morphologies are attracting considerable attention due to their attractive potential applications in the fields of magnetics, catalysis, ferrofluids, high density magnetic recording media; biomedical technology, drugdelivery, colored pigments, medical diagnostics, imaging, synthesis of other nanocomposites and so on. 1-8 Hematite (a-Fe 2 O 3 ) is the most stable, non-toxic, biocompatible, corrosion-resistant magnetic iron oxide under ambient condition and also an n-type semiconductor with 2.1 eV band gap.To date, many efforts have been devoted to control the morphology of a-Fe 2 O 3 by employing different synthesis and processing routes. Rice and cube-shaped a-Fe 2 O 3 structures were reported using the hydrothermal method, 9 while hollow spindle and microsphere a-Fe 2 O 3 , 10 and rhombohedral hematite were prepared by forced hydrolysis. 11 Mitra et al. have synthesized different morphology of a-Fe 2 O 3 by the solvothermal method, 12 whereas Zhang et al. 13 prepared various shaped magnetic microstructures by varying the pH of potassium salt solution. A microwave-assisted hydrothermal process was also used to control shape and aspect ratio of monodisperse a-Fe 2 O 3 nanoarchitectures. 14 Recently, uniform porous a-Fe 2 O 3 nanorods with controlled aspect ratios were synthesized from b-FeOOH nanorods prepared by regulating HCl concentration. 15 Furthermore, 3D flowerlike nanostructures have been self-assembled by an ethylene glycol-mediated process. 16

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Magnetic sensors and the integrator for the magnetic field measurement have been developed for the engineering design of the KSTAR magnetic diagnostics (MDs). The frequency characteristics of a magnetic sensor (for magnetic fluctuation measurement) is investigated from the measurement of the response function of the sensor and the analysis of the equivalent electronic circuit in the frequency range of 10 kHz –15 MHz. An analog integrator, which automatically compensates a drift, is fabricated and its performance test (connected with a magnetic sensor) is carried out under a rf environment. The experimental results from the performance test of the sensor and the analog integrator are presented.

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