FeGaB(25 nm)/Al2O3/FeGaB(25 nm) Multilayer Structures: Effects of Variation of Al2O3Thickness on Static and Dynamic Magnetic Properties

Iron-gallium (FeGa) thin film has the unique advantages in designing integrated magnetic sensors or chips due to its relatively large magnetostrictive constant compared with other soft magnetic materials. In this work, non-magnetic doping and laminating methods have been employed to control the magnetic and electric properties of this alloy film. By doping a certain amount of boron (B), the coercivities are largely decreased for samples of thickness less than ∼30 nm. For thicker films, we find that inserting an ultrathin Al₂O₃ middle layer is very helpful to control the coercivities with negligible influence on saturation magnetization (M_s). The smallest easy-axis coercivity of 0.98×79.6 A/m is obtained in the multilayer film FeGaB(25 nm)/Al₂O₃(0.5 nm)/FeGaB(25 nm). In this case, the resistivity is enhanced by 1.5 times compared with the 50 nm single layer film. Structural characterizations indicate the reductions of crystalline quality and physical dimension of the magnetic grains playing important roles in softening the magnetic properties. Besides, the influences of magnetostatic interaction and morphology characteristics are also considered in facilitating domain reversal. High permeability spectra with gigahertz response are obtained for our multilayer films. The methodology applied here, i.e., enhancing magnetic and electric performance by introducing ultrathin non-magnetic layers, could be translated to other species of soft magnetic materials as well.