Magnetostriction of Dilute Dysprosium Iron and of Gadolinium Iron Garnets

Abstract

λ γ,2 and λε,2 have been measured on a series of partially substituted DyxY1−xIG single crystals between 4.2° and 300°K and in fields up to 110 kOe. Because of the ground-state configuration of the Dy3+ ion (6H15/2) in the crystal field, DyIG has a large magnetostriction. However, since the exchange field on the rare-earth ion is small (Hex ≈ 300 kOe), this magnetostriction is large only at low temperatures. The 4.2°K magnetoelastic energies of the Dy3+ ion in the garnet are: Bγ,2 = λγ,2/2(C11–C12) = − 830 cm−1 and Bε,2 = λ111/4C44 = −1090 cm−1 which are in fact the same order of magnitude as the large energies observed in dysprosium metal. The magnetostriction is found to be linear in Dy concentration, establishing a single-ion source of the magnetostriction. Since the rare-earth exchange field is relatively small, the forced magnetostrictions are extraordinarily large and λ actually decreases from a large value to zero with increasing field strength whenever the iron moment dominates (x < 0.25). To understand these large and unusual temperature and field dependences, crystal-field effects, which affect λγ,2( = 32λ100) and λε,2( = 32λ111) differently, are essential. The magnetostriction in fully substituted GdIG at low temperatures has also been measured. Since the ground state of Gd3+ has zero orbital angular momentum, only a small magnetostriction is expected. This is indeed observed and the magnetostriction of GdIG is of the same magnitude as that of YIG. In particular, at 4.2°K, the contribution of Gd3+ to λγ,2 is 12×10−6, and to λε,2 is 1.8×10−6.