Quest for magnons in ultrathin nickel films

Abstract

High-momentum spin waves (magnons) in ultrathin films of cobalt and iron have been explored thoroughly using inelastic scattering of low-energy electrons. The search for magnons in ultrathin nickel films failed, however, although high-energy magnons do exist in bulk nickel. The failure might be due to the weak coupling of nickel magnons to scattering electrons. In order to increase the coupling we deposited layers of cobalt onto Ni films and successfully studied the magnons of such films. The acoustic modes show the same dispersion as pure Co films, which is consistent with the nearly identical stiffness of bulk magnons in nickel and cobalt. Standing magnons in Ni films covered with Co are strongly damped at the Ni/Cu(100) interface when their total wave vector exceeds about $3\phantom{\rule{0.16em}{0ex}}\mathrm{n}{\mathrm{m}}^{\ensuremath{-}1}$.