Observation of magnetic anisotropy in FeGaB thin films deposited under in-situ applied magnetic field

Multilayer structures based on low damping magnetic films with strong magnetoelastic coupling are attractive candidates for applications in tunable microwave magnetic devices. In particular, surface acoustic wave (SAW) driven heterostructures utilize magnetic resonance and SAW absorption by the magnet. However, magnetic anisotropy plays an important role in the acousto-magnetic couplings, and techniques which allow precise control are needed.

In present work, we use in-situ magnetic fields during sputter deposition to manipulate the structure and anisotropy of the ferromagnet, FeGaB. An Fe₇₁Ga₁₇B₁₂ target was used to deposit 25nm thickness films via RF and DC sputtering. In-situ bias fields up to 100 mT were applied along various crystal axes during growth, and the role of substrate was explored using YZ-cut LiNbO₃, Al₂O₃ (0001) and Si (100). Regardless of field orientation and substrate, all films showed low FMR linewidth (ΔH_FWHM < 34 Oe at 10 GHz) and Gilbert damping (α ~ 4·10^-3), as well as surface roughness below 1nm as characterized by AFM. Importantly though, we find that all films exhibit a uniaxial magnetic anisotropy which correlates with the in-situ field direction. XRD further reveals that, despite the expected amorphous nature of FeGaB, ordering can be seen along the field direction.