Magnetic properties of Fe–Si–B thin films and their application as stress sensors

This study aimed to understand the magnetic behavior of amorphous Fe–Si–B thin films in the presence of residual stress. Residual stress appeared in the thin films during the sputtering process, which was controlled by changing the Ar flow rate during sputtering. Consequently, some thin films developed compressive stress and others developed tensile stress. The residual stress generated in the films ranged from –100 to 400 MPa. The magnetization curves of the samples were measured to extract their magnetic parameters, namely, the magnetic permeability, coercive field, and saturation magnetization. For the films of thickness 500 nm, the relative permeability was higher under tensile stress (µr ∼ 1000) than under compressive stress (µr ∼ 100). A transition between the high and low permeability values occurred for residual stress in the range 0–100 MPa. The relative permeability decreased from 1100 to 800 as the tensile stress increased from 0 to 400 MPa. In addition, the relative permeability decreased from 150 to 100 as the compressive stress increased from 0 to –100 MPa. Moreover, a transcritical state was observed in the samples under compressive stress. For the films of thickness 200 nm, the tensile stress lowered the relative permeability from 800 to 400; however, the compressive stress did not change the permeability significantly.