A STUDY OF AMORPHIZATION IN FE-B MULTILAYERS BY NEUTRON REFLECTOMETRY

The solid state 'amorphisation' reaction in Fe-B multilayer samples ha s been studied in a systematic programme, The Mossbauer spectra of typ ical Fe-B multilayer samples contain the six-line spectrum of alpha-Fe , which disappears after a short period (approximate to 1-2 h) of anne aling at temperatures of about 500-550 K. It is replaced by a paramagn etic 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 amor phisation reaction directly. A Fe70B30 multilayer sample has been give n a real lime, in-situ, annealing treatment at 537 K. The first-order Bragg peak in the neutron reflectivity profiles R(Q) versus Q disappea red with increasing time of anneal, as the elemental layers interdiffu sed. The neutron data were successfully analysed with a structural mod el developed from the Mossbauer measurements. A second neutron experim ent has been made on D17 reflectometer al the ILL, Grenoble, France, u sing pre-annealed samples of Fe60B40 multilayers. Two orders of Bragg peak have been observed in their neutron reflectivity profiles, the an alysis of which confirms that the boron is the principle diffusing spe cies in the reaction. (C) 1997 Elsevier Science S.A.