Nickel-doped nanostructured Fe70Al30 alloys: the role of Ni on the microstructure and the evolution of hyperfine and magnetic properties

Abstract We have investigated the effect of the Nickel concentration on the crystal structure and microstructure, as well as on the hyperfine and magnetic properties of nanostructured (Fe0.7Al0.3)100-xNix powders (x= 0, 5, 10 and 15at.%) fabricated by mechanical alloying. After 72 hours of milling, all the Fe(Al, Ni) samples are single-phase disordered solid solutions with body centred cubic crystal structure. A progressive reduction of the lattice parameter value from 2.9084 A for the Ni-free FeAl binary alloy down to 2.8897 A for the x=15 ternary compound is observed. The mean grain size of the nanocrystals also diminishes down to c.a. 20 nm as the Ni concentration is increased, whereas the mechanically-induced microstrain remains almost constant at around 0.5 %. The magnetic measurements show a ferromagnetic character of all the samples at room temperature with a slight decrease of both saturation magnetization and coercivity as the Ni concentration rises. The fit of Mossbauer spectra collected at room temperature gives an almost constant value (around 26 T) for the mean hyperfine magnetic field, (T). Hence, the addition of Ni to Fe (Ni,Al) solid solution has not a clear influence on the value of , although the hyperfine field distributions suggest somewhat different local environments of Fe atoms.