Tailoring magnetic properties by implantation doping of thin Ni81Fe19 layers

The layer magnetization, the saturation magnetization as well as the magnetic anisotropy and damping behavior of 20 nm thick Ni81Fe19 films have been modified by 30 keV Cr, Ni and Co ion implantation with fluences up to 11016 ions/cm2 ( 5 atom-%). As a function of fluence first an improvement of the (111) fiber texture, then a lattice expansion and finally a partial amorphization of the interface near region of the Ni81Fe19 layer is found. The region of amorphization can be understood quantitatively by the concentration profiles as a function of depth in combination with irradiation induced damage formation. The magnetic properties change correspondingly. Magneto-optic Kerr effect magnetometry and inductive techniques have been used to determine the layer magnetization and the static magnetic anisotropy. A strong reduction of the magnetization with increasing implantation fluence is found. This reduction can be decomposed in a reduction of the active magnetic layer thickness and a reduction of the saturation magnetization. The latter one has been determined by means of pulsed inductive microwave magnetometry. This technique allows in addition the determination of the dynamic anisotropy, the relaxation rate and the magnetic damping constant. A reduction in magnetic anisotropy and a strong increase of the magnetic damping behavior is observed as a function of implantation fluence which is mainly attributed to doping effects. However, also radiation induced damage effects have to be considered in order to fully understand the change in magnetic properties.