A reactor comprising an annular iron core constituting a closed magnetic path and a conductor wound on the annular core, said iron core being formed of {HEAD ~ particles} of {TAIL ~ iron} or an iron based magnetic material each covered with an insulative oxide film which contains 0.3 to 0.8% of oxygen by weight based on the particle 
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A reactor comprising an annular iron core constituting a closed magnetic path and a conductor wound on the annular core , said iron core being formed of { HEAD ~ particles } of { TAIL ~ iron } or an iron based magnetic material each covered with an insulative oxide film which contains 0.3 to 0.8 % of oxygen by weight based on the particle
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