Magnetically ordered fcc structure at the relaxed grain boundaries of pure nanocrystalline Fe

Pure Fe powders, milled down to 10 nm crystallite size, have been analyzed by a combination of Mossbauer spectroscopy. high resolution transmission electron microscopy, and magnetization measurements. After annealing the as-milled powders at 570 K for 1 hour, a new phase is identified with a hyperfine field of 21 T, a lower magnetic moment than bulk Fe, a magnetic order-disorder transition temperature of about 500 K, and a fee crystal structure. It is tentatively interpreted as a new magnetically ordered phase of Fe. [S0031-9007(98)07721-7].