Ferromagnetic resonance study of polycrystalline Cobalt ultrathin films

TL;DR

This study investigates ferromagnetic resonance in polycrystalline cobalt ultrathin films, analyzing how film thickness and deposition method affect magnetic properties and damping, with implications for spintronic applications.

Contribution

It provides a comparative analysis of FMR properties of evaporated and sputtered Co films, highlighting the influence of fabrication method on magnetization and damping.

Findings

Linewidth increases below 3 nm thickness

Sputtered films exhibit higher damping for <4 nm thickness

Interface spin mixing conductance is deduced from linewidth data

Abstract

We present room temperature ferromagnetic resonance (FMR) studies of polycrystalline ||Pt/10 nm Cu/t Co/10 nm Cu/Pt|| films as a function of Co layer thickness (1 < t < 10 nm) grown by evaporation and magnetron sputtering. FMR was studied with a high frequency broadband coplanar waveguide (up to 25 GHz) using a flip-chip method. The resonance field and the linewidth were measured as a function of the ferromagnetic layer thickness. The evaporated films exhibit a lower magnetization density (Ms = 1131 emu/cm^3) compared to the sputtered films (Ms= 1333 emu/cm^3), with practically equal perpendicular surface anisotropy (Ks ~ -0.5 erg/cm^2). For both series of films, a strong increase of the linewidth was observed for Co layer thickness below 3 nm. For films with a ferromagnetic layer thinner than 4 nm, the damping of the sputtered films is larger than that of the evaporated films. The thickness dependence of the linewidth can be understood in term of the spin pumping effect, from which the interface spin mixing conductance g^{\uparrow\downarrow}S^{-1} is deduced.