Single magnetic domain Terfenol-D microstructures with passivating oxide layer

Abstract Studies on giant magnetostrictive intermetallic compound Tb0.3Dy0.7 Fe1.92 (Terfenol-D) thin films are gaining increasing attention due to the interest in small scale magnetic structures. In this work, polycrystalline Terfenol-D thin films (60 nm) are produced using a Direct Current (DC) magnetron sputtering process and a hybrid thermal annealing approach, i.e. substrate heating and post-annealing. The crystallized Terfenol-D films are micropatterned (3 μm and 20 μm diameters) using a photolithographic method followed by Argon etching. The continuous and micropatterned thin films are characterized with XRD, SQUID and MOKE magnetometers showing properties similar to bulk polycrystalline Terfenol-D. Additional studies are conducted using X-ray absorption spectroscopy and the X-ray magnetic circular dichroism to investigate oxidation. Results show that while the top surface of these Terfenol-D structures are capped with Ta thin films, the side walls of the structures are exposed to ambient atmosphere raising the concern of oxidation issues. This work shows that a passivating oxide layer forms on the side walls of these small-scale Terfenol-D disks which is attributed to both the Ta capping layer as well as residual stresses preventing continued stress corrosion cracking caused by the oxidation process.