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 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 {HEAD ~ weight} based on the particle 
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 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 { HEAD ~ weight } based on the particle
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