Magnetic and structural characterization of mechanically alloyed Fe_50-Co_50 samples.

Abstract

Samples of nominal composition Fe50Co50 were produced by mechanical alloying by using a planetary ball mill and different milling times. The samples were studied via X-ray diffraction, Mössbauer spectroscopy, and X-ray photoelectron spectroscopy to characterize the phase distribution resulting from the milling process. The Mössbauer data indicated that Co starts diffusing into Fe after 8 h of milling. Between t = 8h and t = 24 h the sample has a heterogeneous composition, presenting a bimodal hyperfine field distribution with maxima centred at 34.3 T and 35.8 - 36.4 T, compatible with the presence of different Fe environments (richer in Co and richer in Fe, respectively). After 48 h of milling, the sample presents a more homogeneous composition showing an almost symmetric hyperfine magnetic field distribution centred at H=34.9 T, indicating that a disordered equiatomic FeCo solid solution has already been formed. The X-ray photoelectron spectroscopy data indicate that the native oxide layer formed on the freshly milled samples contains Co2+, Fe2+ and Fe3+ oxides. After complete removal of this native oxide layer by Ar ion bombardment, X-ray photoelectron spectroscopy analysis yields the composition of the nominal equiatomic Fe50Co50 alloy.