It is preferred that {HEAD ~ the cage} of the present invention has {TAIL ~ an oxide layer} comprising an Fe3O4 phase as a main ingredient and not containing an Fe2O3 phase to a thickness of 50 nm or more nearer to a further surface on the nitride layer 
It is preferred that { HEAD ~ the cage } of the present invention has { TAIL ~ an oxide layer } comprising an Fe3O4 phase as a main ingredient and not containing an Fe2O3 phase to a thickness of 50 nm or more nearer to a further surface on the nitride layer
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH