Study on correlation between magnetic properties and stress in ultrathin transition metal films

Abstract

The area of ultrathin ferromagnetic films has attracted considerable attention during the last a few decades, due to their novel physical properties and diverse technological applications (magnetic recording and magnetic random access memory (MRAM), etc.). In particular, searching for magnetic multilayer films exhibiting room-temperature perpendicular magnetic anisotropy (PMA), where magnetization is perpendicular to the film plane, has been the significant recent interests from fundamental aspects to understand spin orientation as well as technical applications to ultrahigh-density magnetic and magneto-optical recording. In this study, we report the experimental observation of room-temperature PMA in Ni/Pd(111) nanomultilayer films having the thickness range of 5-11 Å Ni and 4-11 Å Pd sublayers, prepared by dc magnetron sputtering on glass substrates at Ar sputtering pressure of 7 mTorr. PMA was found to be sensitively dependent on both Ni- and Pd-sublayer thicknesses, and a maximum anisotropy energy of $5.6×10^5erg/㎥$ was obtained for $(5-Å Ni/6-Å Pd)_30$ multilayer. The magnetoelastic anisotropy was quantitatively determined from in situ stress and ex situ magnetostriction coefficient measurements to reveal an origin of observed PMA in Ni/Pd nanomultilayers. It was found that the magnetoelastic anisotropy plays an important role for the observed PMA in this system, together with the surface anisotropy. However, all the Ni/Pd nanomultilayers prepared at an Ar sputtering pressure of 2 mTorr show in-plane magnetic anisotropy. We have found that the observed easy-axis reorientation from in-plane to out-of-plane as varying the Ar sputtering pressure could be ascribed to the enhancements of the surface anisotropy as well as the stress-induced magnetoelastic anisotropy. Magnetization study of Ni/Pd nanomultilayer films, prepared at 7 mTorr Ar sputtering pressure, revealed that the magnetization in Ni/Pd nanomultilayers was effectively enhanced, due to the polariza...