Magnetization reversal and spin waves in exchange coupled NiFe/Cu/Co nanodisks

Abstract

We present an experimental study of the static and high frequency dynamic properties of NiFe(10 nm)/Cu(tCu)/Co(10 nm) nanometric disks for different values of the Cu spacer thickness (tCu=0.7, 1.2, and 2.0 nm). We found that the exchange interlayer coupling dominates over the dipolar interaction favoring parallel alignment between the two layers of magnetization with formation of vortex states at remanence. Brillouin light scattering technique from thermally excited spin waves was used to estimate the value of the interlayer exchange coupling in the unpatterned NiFe/Cu/Co films as well as to investigate the magnetic normal modes in the corresponding multilayered nanodisks. In the latter case, evidence is given for a discretization of the measured spectrum with reduction in the mode frequency associated to the demagnetizing effect induced by lateral confinement. Micromagnetic simulations indicate that these discrete modes correspond to an in-phase precession of the magnetization in the two ferromagnetic layers while, at variance with the continuous film, no evidence of optical modes is obtained.