Magnetostriction of Gd-Tb alloys

Abstract

The work described in this thesis is directed towards study of the magnetostriction in the Gd-Tb alloy system using resistive strain gauge technique. The experiments were carried out at various ranges of temperatures between 4.5 K and 250 K, and magnetic fields up to 13 Tesla were available. High quality single crystals of Gd(_0.95)Tb(_0.05') Gd(_0.80)Tb(_0.20')Gd(_0.50)Tb(_0.50), and Gd(_0.25)Tb(_0.75) were used to measure the four magnetostriction coefficients λ(^y,2), λ(^a,2)(_2), λ(^a,2)(_1) and λ(^E,2) temperature dependences of the magnetostriction coefficients were fitted with both single-ion mechanism and a theory containing a term representing a two-ion interaction. Only the values of the magnetostric tion coefficients for the samples containing high concentration of Terbium obey the single-ion I5/2 [ £(^-1)(m(_n))]. However, the experimental results were better fitted using the other theory, but in most cases the fit was less close than could have been desired. An anomalous behaviour was observed for the samples containing 5% and 20% of Terbium in the magnetostriction curves along the c-axis, 45 to c-axis, and b-axes in the b-c plane. These anomalies disappeared by raising the field and temperature above 70-K. Another anomaly was observed in the temperature dependence of λ(^a,2)(_2) for the sample containing 20% of Terbium where a very sharp peak was obtained for this coefficient at 60 K. The variation of the coefficients λ(^y),2, λ(^a,2)(_2) with alloy composition were able to be represented using an exponential relation, while a linear relation was found for the coefficient λ(^a,2)(_I). The values of the coefficients extrapolated well to the values of the pure metalsgiven by previous workers. The ratio λ(^e,2)(o) / λ(^y,2)(_o) was found to have anomalously large values compared with that expected for the heavy rare earth metals and increase with increasing Terbium concentration in the alloy.