Magnetically Ordered fcc Structure at the Relaxed Grain Boundaries of Pure Nanocrystalline Fe

Abstract

Pure Fe powders, milled down to 10 nm crystallite size, have been analyzed by a combination of M\"ossbauer 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 fcc crystal structure. It is tentatively interpreted as a new magnetically ordered phase of Fe.