Magnetization and Magnetic Anisotropy of Co/W Multilayers

Abstract

The magnetic properties of polycrystalline Co/W multilayers have been investigated using angular-dependent ferromagnetic resonance (FMR) and SQUID magnetometry. Two sets of samples with a constant thickness of Co layers (CoI: dCo = 1 nm and CoII: dCo = 2.5 nm) and varying W layer thickness (1 to 7 nm) were studied. The structure of the multilayers was analysed by X-ray reflectivity (XRR) and X-ray diffraction (XRD). We found a well-defined 〈110〉 texture and coherent structure of the multilayers. The saturation magnetization of Co is smaller than that of bulk Co which is explained by a reduced Co moment at the interfaces of more than 50%. A narrow FMR linewidth on the order of 200 Oe at 9.5 GHz is observed for CoI and CoII multilayers with dW ≈ 1 nm that indicates the high magnetic homogeneity of the Co layers. The second and fourth-order magnetic anisotropy constants (K2, K4⟂) are found to be independent of the Co layer thickness. K2 is inversely proportional to the W layer thickness, which is due to the changing lateral lattice mismatch with the W layers.