TRANSMISSION ELECTRON-MICROSCOPY OF TERFENOL-D CRYSTALS

Magnetic domain and microstructure observations are presented from sam ples of pseudo-single-crystal Terfenol-D examined by transmission elec tron microscopy (TEM). This ternary alloy is of significant technologi cal interest since it exhibits the highest known magnetostriction to a nisotropy ratio near room temperature. Specimens for TEM studies in (1 10), (111), and (112) orientations have also Shown regions of unusual diffraction contrast in bright field which appears to be very sensitiv e to specimen tilt. Lorentz mode TEM has subsequently shown such regio ns to correspond exactly with magnetic domains. This contrast is attri buted to the high magnetostrictive strain causing a local distortion o f the lattice and thus a local deviation from the Bragg condition. Thi s conclusion has been investigated and supported by TEM observations w ith the samples cooled below the spin reorientation temperature. When this transition is reached the diffraction contrast in bright field is considerably decreased and cannot be made to vary by tilting the spec imen. The latter experiments also indicate that the change from [111] to [100] easy axis is not a well-defined one but, rather, that the spi n reorientation is a sluggish change. High-resolution lattice images s how the coherency of the twin boundaries. (C) 1996 American Institute of Physics.