57Fe NMR study of amorphous and rapidly quenched crystalline Fe-B alloys

Amorphous and crystalline Fe-B alloys (5–25 at % B) were studied using pulsed ⁵⁷Fe nuclear magneticr esonance at 4.2 K. The alloy samples were prepared from a mixture of the ⁵⁷Fe and ¹⁰B isotopes by rapid quenching from the melt. In the microcrystalline Fe-(5–12 at %) B alloys, the resonance frequencies were measured for local states of ⁵⁷Fe nuclei in the tetragonal and orthorhombic Fe₃B phases and also in α-Fe. The resonance frequencies characteristic of ⁵⁷Fe nuclei in α-Fe crystallites with substitutional impurity boron atoms in the nearest neighborhood were also revealed. In the resonance frequency distribution P(f) in the amorphous Fe-(18–25) at % B alloys, there are frequencies corresponding to local Fe atom states with short-range order of the tetragonal and orthorhombic Fe₃B phases. As the boron content decreases below 18 at %, the P(f) distributions are shifted to higher frequencies corresponding to ⁵⁷Fe NMR for atoms exhibiting a short-range order of the α-Fe type. The local magnetic structure of the amorphous Fe-B alloys is also considered.