A study of magnetic properties in CoFeSiB amorphous thin films submitted to furnace annealing

Co67Fe4Si14.5B14.5 amorphous thin films have been produced by rf sputtering with thickness varying from 30 nm to 90 nm. Differential scanning calorimetry and X‐ray diffraction have been employed to reveal a predominant amorphous phase in the as‐prepared samples, although a small crystalline fraction cannot be excluded. Selected specimens have been submitted to furnace annealing in vacuum with and without the application of an in‐plane magnetic field with an intensity of 100 Oe. At temperatures ≥550 °C the thin films develop a significant crystalline fraction responsible of the large increase of the coercivity of their magnetic hysteresis loops. Thicker films develop larger coercivities upon crystallization. Field annealing below the Curie temperature of the alloy results in the induction of a uniaxial magnetic anisotropy (rectangular hysteresis loop along the easy axis, almost linear loops along the hard axis). Sample thickness and annealing time affect the development of the uniaxial anisotropy and the remanence to saturation ratio. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)