A cage 1, wherein an oxide layer comprising an Fe3O4 phase as a main ingredient and not containing or Fe2O3 phase is present at a thickness of {HEAD ~ 50 nm} or more further on the surface of {TAIL ~ the nitride layer} 
A cage 1 , wherein an oxide layer comprising an Fe3O4 phase as a main ingredient and not containing or Fe2O3 phase is present at a thickness of { HEAD ~ 50 nm } or more further on the surface of { TAIL ~ 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 OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL