Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy

Transition metal ferromagnetic films with perpendicular magnetic anisotropy (PMA) have ferromagnetic resonance (FMR) linewidths that are one order of magnitude larger than soft magnetic materials, such as pure iron (Fe) and permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The FMR linewidth depends linearly on frequency for perpendicular applied fields and increases significantly when the magnetization is rotated into the film plane. Irradiation of the film with Helium ions decreases the PMA and the distribution of PMA parameters. This leads to a great reduction of the FMR linewidth for in-plane magnetization. These results suggest that fluctuations in PMA lead to a large two magnon scattering contribution to the linewidth for in-plane magnetization and establish that the Gilbert damping is enhanced in such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for pure Fe)

Longitudinal and transverse magnetization components in thin films: A resonant magnetic reflectivity investigation using circularly polarized soft x-rays

An in-plane vectorial analysis of the magnetization of thin magnetic films is presented. Longitudinal soft x-ray resonant magnetic reflectivity curves display characteristic nodes where the longitudinal scattering component is suppressed by x-ray interference. The transverse magnetic component can be effectively retrieved at these nodal points, despite the use of circular polarization and longitudinal scattering geometry. Using a single geometric configuration, transverse and longitudinal magnetic hysteresis loops can be clearly separated. Calculations based on a Stoner-Wohlfarth model satisfactorily describe both loops. Therefore, this method presents a viable alternative to standard vectorial analysis techniques, with the additional benefit of element specificity.X1143sciescopu

Role of the nonmagnetic layer in determining the Landeacute g-factor in a spin-transfer system

The microscopic origin of the Landeacute g-factor in two ferromagnetic/nonmagnetic (FM/NM) bilayer systems-Co/Cu and Ni/Pd-has been investigated using x-ray magnetic circular dichroism, resonant magnetic reflectivity, and band calculations. The FM/NM bilayer represents the building block of any complete spin-transfer structure (FM1/NM/FM2). The valence electronic structure is profoundly altered over a finite length across the FM/NM interface. A considerable charge transfer takes place from the NM to the FM material. This results in an enhancement of the orbital-to-spin magnetic moment ratio in the FM layer and an induced magnetic polarization in the NM layer. Both effects turn out to be crucial for a correct understanding of the g-factor in spin-transfer systems.X1170sciescopu

Giant magnetoresistance by exchange springs in DyFe2/YFe2 superlattices

Magnetization and magnetoresistance measurements are reported for antiferromagnetically coupled DyFe2/YFe2 multilayers in fields up to 23 T. It is demonstrated that the formation of short exchange springs ( ~20 Å) in the magnetically soft YFe2 layers results in a giant magnetoresistance as high as 32% in the spring region. It is shown that both the magnitude of the effect and its dependence on magnetic field are in good agreement with the theory of Levy and Zhang for domain wall induced giant magnetoresistance