Ab initio calculation of the giant magnetostriction in terbium and erbium

The single-ion 4f contributions to the components lambda(2)(alpha 2), lambda(gamma 2), and lambda(1)(alpha,2) Of the giant magnetostriction tensor of Tb and Er are calculated ab initio by a constrained density-functional theory in the local spin-density approximation and the full-potential linear-muffin-tin-orbital method. The data exhibit the expected change in sign when going from To with an oblate 4f charge density to Er with a prolate 4f charge density. The satisfactory agreement with experimental results shows that the giant magnetostriction in Tb and Er is dominated by the single-ion 4f contribution.