A New Class of Materials for Magneto-Optical Applications: Transparent Amorphous Thin Films of Fe–B–Nb and Fe–B–Nb–Y Metallic Glassy Alloys

Optically highly transparent, soft magnetic thin films (4-18 nm thick) of Fe-B-Nb and Fe-B-Nb-Y-based glassy metal targets were grown on quartz substrates by pulsed laser deposition, and their optical and magneto-optical properties were investigated over the visible spectrum (400-700 nm). All the films found to be fully amorphous in structure were continuous with uniform thickness and surface morphology. Their optical transmittance in the range 50%-85% was found to be film thickness dependent over the entire visible regime. The Verdet constant (V) and Faraday rotation angle (θ_f ) for different films (~4-18 nm) investigated as a function of wavelength (λ) show considerably higher values for the films of Fe-B-Nb-Y alloy as compared with those for Fe-B-Nb films, e.g., the ~4 nm film of Fe-B-Nb-Y alloy exhibits V ~ 49°/Oe cm and θ_f ~ 26°/μm while it decreased to ~29.4°/Oe and ~11.8°/μm, respectively, for the Fe-B-Nb alloy at λ = 611 nm. A linear relationship is found for the wavelength dependence of V and θ_f for both alloy systems. To the best of our knowledge, these values are considerably higher than those reported for any other magneto-optic material. The films are found to be soft magnetic with a high saturation moment while their magnetic coercivity values increases with thinness of the films. The observed combination of optical and magneto-optical properties of this new class of amorphous metallic films makes them viable for multifunctional magneto-optical applications.