Dopants for independent control of precessional frequency and damping in Ni81Fe19 (50 nm) thin films

Dilute impurities can be used to control the dynamical response of ferromagnetic thin film magnetization at frequencies >1 GHz. Central lanthanide dopants (Sm, Eu, Tb, Dy, and Ho) have been investigated for their effect on the magnetization dynamics of ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ (50 nm). We find that Sm, Dy, and Ho contribute an increase on damping α up to four times stronger per concentration than that provided by Tb, with minimal effect on precessional frequency. One dopant, Eu, leaves α unchanged but boosts the resonant frequency $f_p$ of the system by ∼500 MHz for 3% addition, equivalent to a dynamic anisotropy field of 9 Oe, “stiffening” the system. The results indicate that precessional frequency and damping may be controlled independently in magnetoelectronic device materials.