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