A series of ͑Fe 100−y Ga y ͒ 1−x B x ͑x =0-21 and y =9-17͒ films were deposited; their microstructure, soft magnetism, magnetostrictive behavior, and microwave properties were investigated. The addition of B changes the FeGaB films from polycrystalline to amorphous phase and leads to excellent magnetic softness with coercivity Ͻ1 Oe, high 4M s , self-biased ferromagnetic resonance ͑FMR͒ frequency of 1.85 GHz, narrow FMR linewidth ͑X band͒ of 16-20 Oe, and a high saturation magnetostriction constant of 70 ppm. The combination of these properties makes the FeGaB films potential candidates for tunable magnetoelectric microwave devices and other rf/microwave magnetic device applications.