MAGNETICALLY ORDERED FCC STRUCTURE AT THE RELAXED GRAIN-BOUNDARIES OFPURE NANOCRYSTALLINE FE

Pure Fe powders, milled down to 10 nm crystallite size, have been anal yzed by a combination of Mossbauer spectroscopy. high resolution trans mission electron microscopy, and magnetization measurements. After ann ealing the as-milled powders at 570 K for 1 hour, a new phase is ident ified with a hyperfine field of 21 T, a lower magnetic moment than bul k Fe, a magnetic order-disorder transition temperature of about 500 K, and a fee crystal structure. It is tentatively interpreted as a new m agnetically ordered phase of Fe. [S0031-9007(98)07721-7].