Fe-based amorphous thin films of two compositions (Fe₈₀ and Fe65.6Co9.4B25) were deposited by RF magnetron sputtering with and without applying an in situ magnetic field along the films' in-plane direction. In addition, films with varying thickness were deposited for each composition. Hysteresis loops and residual stress were measured and compared to study the effect of in situ fields on the magnetic and magnetostrictive behavior of the films. Results showed that in situ magnetic fields can lower the in-plane coercivity for the Fe₈₀ films. Also, when the residual stress was below a certain level, its distribution in different directions shows a uniaxial feature due to the applied in situ field. This uniaxial distribution of stress adds an extra magnetoelastic anisotropy to the films. This paper provides insight for optimizing magnetic thin films' properties for applications where the magnetostriction is relevant, in terms of the in situ magnetic field, coercivity, and residual stress. IEEE