Positron annihilation in FeAl alloys

Abstract

The effect of localized magnetic moments on the positron annihilation was first found in dilute solid solutions of Fe in Pd (1). The concentration dependence of the relative probability for positron annihilation with conduction electrons (W ) in CoAl alloys has shown (2) that in the range of stoichiometric composition the W value is essentially increased. This feature may be accounted for by the positron interaction with structural vacancies and the localized electronic states. The existence of localized magnetic states in CoAl alloys with slight excess of cobalt atoms (50.5 at% co) was confirmed by nuclear magnetic resonance experiments (3). P P Some information has been reported (4) about the formation of localized magnetic moments in FeAl alloys in the range of stoichiometric composition and the present investigation has been undertaken to study their effect on the positron annihilation parameters. The experiments were carried out for FeAl alloys with b.c.c.CsCl type structure containing 32 to 52 at% Al.FeAl alloys with 48, 49, 50, 51, and 52 at% A1 were obtained by melting carbonyl iron and high-purity aluminium in an induction furnace in argon atmosphere. Subsequent chemical analysis has indicated that alloy compositions differ slightly from the above mentioned values. The ingots were subjected to homogeneizing annealing in vacuum at 1000 C for 24 h. The samples were cut from the inner part of ingots.Angular distribution curves for 2 r positron annihilation in FeAl alloys were measured using a VA-64 apparatus. 0 Fig. 1 shows the dependence of the relative probability for positron annihilation with conduction electrons on concentration. It is seen clearly that the alloy with 51 at% Fe has a W value by % 10% larger than that for the rest of alloys under investigation for which W is about the same. P P Previously studied CoAl alloys (2) exhibit the presence of structural vacancies for concentrations with excess A1 atoms (compared with the equi-atomic composition)

The preparation of narrow-line M$ouml$ssbauer sources of 57Co in metallic matrices

“…Palladium can retain quenched-in iron-vacancy clusters when quenched from near 900 "C and the broadening produced by these is very pronounced (Dekhtyar et al 1969). The alloys cool rapidly in the argon arc furnace and we have found it necessary to anneal both palladium and platinum samples at about 500 "C in order to obtain the best linewidths.…”

The recovery of Quenched‐in Vacancies in Fe–Al (6.3 to 28.3 at.%) Alloys studied by Positron Annihilation

“…The peak height and the Doppler parameter (but not the lifetime) exhibit an abnormally strong decrease a t 400 "C and a new increase above 400 "C. The cause of this effect is not clear until now. Positron annihilation studies of higher concentrat>ed Fe-A1 alloys (33 to 51 at.% Al) can be found in the literature (WEBER et al;MEURTTN, LESBATS;DEKHTYAR et al 1973DEKHTYAR et al , 1979.…”

Positron annihilation and mössbauer effect in dilute solid solution of Ni, Pd, and Pt with iron

“…In the presence of Fe impurities in the solid solutions of W the thermalized positrons are trapped by these impurities and the annihilation velocity is changed around impurity atoms (1,2). If 2 is the annihilation velocity in the pure matrix 2 and A i s the annihilation velocity ih the vicinity of the impurity atom, the fraction of trapped positrons E l ) i s given by 1 where 3c. is the capture rate, c .…”