Magnetization and Magnetic Anisotropy of Co/W Multilayers

Abstract

The magnetic properties of polycrystalline Co/W multilayers have been investigated using angulardependent ferromagnetic resonance (FMR) and SQUID magnetometry. Two sets of samples with a constant thickness of Co layers (CoI: d Co ¼ 1 nm and CoII: d Co ¼ 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 h110i 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 d W % 1 nm that indicates the high magnetic homogeneity of the Co layers. The second and fourthorder magnetic anisotropy constants (K 2 , K 4? ) are found to be independent of the Co layer thickness. K 2 is inversely proportional to the W layer thickness, which is due to the changing lateral lattice mismatch with the W layers.

Structural and magnetic properties of amorphous Co-W alloyed nanoparticles

“…In other Co-W multilayer systems, the origin of the magnetic anisotropy observed is ascribed to the surface of the Co layers 75,76 and to volume-type strain anisotropy. 75 However, we have demonstrated that interface effects play no role in the increase of K eff obtained for our Co-W NPs, compared to the bulk Co value.…”

Magnetic Nanoparticles

“…In other Co-W multilayer systems the origin of the magnetic anisotropy observed is ascribed to the surface of the Co layers [59,60] and to volume-type strain anisotropy [59]. However, we have demonstrated that interface effects play no role in the increase of K eff obtained for our Co-W NPs, compared to the bulk Co value.…”

“…This measurement system consists in probing the ac magnetic susceptibility of a material in one direction while an external bias magnetic field is applied perpendicular to the measurement direction. Analysis of the TS in magnetic materials have demonstrated its potential and versatility to study singular magnetic properties of bulk [50][51][52], single crystals [53], thin films [54][55][56][57] and nanoparticles (NPs) systems [58][59][60][61][62]. TS measurement techniques developed up to date are based on conventional inductance susceptibility techniques [60,63,64], magneto-optical setups [54,57] and self-resonant circuits in the radio frequency (RF) range [65].…”

Structural and Magnetic Properties of Amorphous Co–W Alloyed Nanoparticles

“…75 However, we have demonstrated that interface effects play no role in the increase of K eff obtained for our Co-W NPs, compared to the bulk Co value. Our Co-W NPs have an oblate shape with semiaxes a = D eff PV /2 and c = D eff CS /2, albeit with a small c/a ratio; in the two samples for which the plan-view and crosssection average diameter could be determined (see Table I), c/a ≈ 0.93 (1).…”