Domain observation and magnetostriction in Tb0.3Dy0.7Fe2 twinned single crystals

Abstract

The ternary alloy Tb_0.3Dy_0.7Fe₂ (Terfenol‐D) exhibits the largest known magnetostriction to anisotropy ratio near room temperature. To better determine the interaction between the elastic and magnetic properties of this material, a stoichiometric twinned single crystal was grown by a free‐standing float‐zone technique. Observations using Scanning electron microscopy and energy dispersive spectroscopy confirmed that the sample was free of the normally present rare‐earth (RE) eutectic phase and simultaneously free of Widmanstatten precipitate (RE Fe₃). A bar with (111) and (11̄0) faces perpendicular to the [112̄] growth direction was examined. Also, a [111̄] slab was cut from the boule. This slab was studied along the [111̄] and [11̄0] directions with prestress applied along the [111̄]. This is the first report of the effects of applying prestress and magnetic fields in a direction not collinear with the [112̄] growth direction. From magnetization (M) and magnetostriction (λ) measurements as a function of field, prestress, and temperature, we determined the hysteresis and saturation parameters. These measurements do not indicate the [11̄0] λ and M behaviors found previously for RE‐rich Terfenol‐D. Domain observations with differential phase contrast and x‐ray topography have shown different orientations in the twin and parent sections of the [111̄] specimen. The observed structures can be interpreted as arising from domains with magnetization components normal to the surface. The domain observations on the (111) and (11̄0) bar faces and on the [111̄] slab correlate with each other with respect to orientations and domain interpretations.