Stress dependence of soft, high moment and nanocrystalline FeCoB films

Abstract

Soft, high moment materials are crucial for the magnetic data recording industry in applications such as write poles and soft underlayers. Ever increasing areal densities have pushed the requirements for materials exhibiting saturation magnetizations above 2 T. In this work we investigate nanocrystalline FeCoB which exhibits a saturation magnetization of ∼2.2 T. FeCoB exhibits a magnetostriction of >50×10−6 which suggests that the magnetoelastic anisotropy is important. Nanocrystalline FeCoB films are rf diode sputtered as a function of Ar pressure. As the pressure is increased, film stress increases from compressive to tensile with a critical pressure of ∼12 mTorr. TEM and XRD show that pressure has no significant effect on microstructure, however, at pressures above a critical pressure, the FeCoB films change from magnetically isotropic to magnetically uniaxial with low coercivity. This is due entirely to the magnetoelastic anisotropy which must be considered as the industry begins to utilize magnetic alloys with nonzero magnetostriction.