A study of amorphisation in Fe-B multilayers by neutron reflectometry

The solid state ‘amorphisation’ reaction in Fe-B multilayer samples has been studied in a systematic programme. The Mössbauer spectra of typical Fe-B multilayer samples contain the six-line spectrum of α-Fe, which disappears after a short period (1–2 h) of annealing at temperatures of about 500–550 K. It is replaced by a paramagnetic component which can be confidently identified with the growth of the amorphous phase. Neutron reflectometry experiments have been made on the CRISP instrument at the ISIS neutron source to follow this amorphisation reaction directly, A Fe70B30 multilayer sample has been given a real time, in-situ, annealing treatment at 537 K. The first-order Bragg peak in the neutron reflectivity profiles R(Q) versus Q disappeared with increasing time of anneal, as the elemental layers interdiffused. The neutron data were successfully analysed with a structural model developed from the Mössbauer measurements. A second neutron experiment has been made on D17 reflectometer at the ILL, Grenoble, France, using pre-annealed samples of Fe60B40 multilayers. Two orders of Bragg peak have been observed in their neutron reflectivity profiles, the analysis of which confirms that the boron is the principle diffusing species in the reaction.