Resolving the controversy of a possible relationship between perpendicular magnetic anisotropy and the magnetic damping parameter (original) (raw)
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Higher-order perpendicular magnetic anisotropy and interfacial damping of Co/Ni multilayers
Physical Review B
We report on the experimental investigation of the perpendicular magnetic anisotropy in Pt/[Co/Ni] N /Ir multilayers. Broadband ferromagnetic resonance (FMR) and polar angle dependent FMR measurements reveal the presence of a strong fourth-order contribution to the perpendicular anisotropy. By numerically solving the Smit-Beljers relation, we are able to fit the polar angle dependence of the resonance field and extract both the second and fourth-order anisotropy constants. While this model provides a qualitative description for all samples, we note that, for samples near or in the easy cone state of the phase diagram, systematic deviations emerge in the polar angle dependent data. The exchange stiffness of the multilayers is found to be lower than the weighted average of the exchange stiffness reported for Co and Ni in the literature. We find that the effective Gilbert damping scales with the inverse multilayer thickness, indicating a significant interfacial contribution to the damping process.
Physical Review B, 2012
We performed a systematic study of damping in Co 90 Fe 10 /Pd multilayers by use of broadband (1-60 GHz) ferromagnetic resonance (FMR) spectroscopy in the perpendicular geometry. The data were fitted with the conventional Landau-Lifshitz equation in conjunction with an inhomogeneous contribution to linewidth H 0. Samples were prepared with net perpendicular anisotropy field values ranging from −0.5 to +1.2 T. H 0 shows a dependence on the perpendicular anisotropy, though the Landau-Lifshitz damping parameter α, which ranged from 0.016 to 0.04, exhibits no trend as a function of anisotropy. We explain the wide variation of α as a result of spin pumping from Co 90 Fe 10 into adjacent nonmagnetic layers. We use a quantitative model for spin pumping that includes the intrinsic spin-mixing conductance at the Co 90 Fe 10 /Pd interface and the spin-diffusion length of Pd, which were experimentally measured at room temperature to be (1.07 ± 0.13) × 10 19 m −2 and 8.6 ± 1.0 nm, respectively. We quantitatively show how α is enhanced by spin pumping through an FMR investigation of individual Pd/CoFe/Pd, and Pd/CoFe/Pd/CoFe/Pd layer structures.
Applied Physics Letters, 2013
The relationship between Gilbert damping and magneto-crystalline anisotropy is studied here using an all-optical method in a perpendicular Co/Ni multilayer system by varying the Ti-buffer thickness. As the Ti-buffer thickness increases, the magneto-crystalline anisotropy is enhanced. The time-resolved Kerr signal of each sample is well described by its own intrinsic Gilbert damping constant in a wide range of the external magnetic field. Interestingly, we find that Gilbert damping constants increase linearly from 0.021 to 0.036 when the magneto-crystalline anisotropy of the samples varies from 2.4 to 3.4 Merg/cm 3 . Such a linear relationship implies that the spin-orbit interaction is the main source of the damping process through spin-lattice relaxation in our system. V C 2013 AIP Publishing LLC.
Physical Review B, 2013
We use broadband ferromagnetic resonance spectroscopy and x-ray diffraction to investigate the fundamental origin of perpendicular anisotropy in Co 90 Fe 10 /Ni multilayers. By careful evaluation of the spectroscopic g-factor, we determine the orbital moment along the out-of-plane and in-plane directions. For the multilayers, we find a direct relationship between the orbital moment asymmetry and the perpendicular anisotropy, consistent with the theory of Bruno [P.Bruno, Phys. Rev. B, 39, 865 (1989)]. A systematic x-ray diffraction study revealed the presence of a trigonal strain as high as 0.7 % in some samples. However, we found no direct correlation between the strain and the anisotropy, indicating that the anisotropy is not dominated by magnetoelastic effects. In order to further study the interface structure on the anisotropy, we prepared a set of equivalent alloy samples. The strain in the alloy samples was comparable to that of the multilayer samples; however the orbital moment asymmetry in the alloy samples showed a very different trend allowing us to isolate the effect of the interfaces in the multilayers.
Journal of Magnetism and Magnetic Materials, 2017
We present a study of perpendicular magnetic anisotropy in [Co/Ni(t)/Co/Pt] ×8 multilayers for use as free layers in magnetic tunnel junctions (MTJ) and spin valves. The thickness t of the Ni sub-layer was varied and the resulting magnetic properties were compared with (Co/Ni) and (Co/Pt) multilayers with the same number of repeats. As determined from magnetic force microscopy and magnetometry measurements, all multilayers exhibited a perpendicular magnetic anisotropy with an increase of saturation magnetization with thickness t. From the temperature dependence of the magnetization, well described by a Bloch law, we find that the spin-wave stiffness constant of the [Co/Ni(t)/Co/Pt] ×8 multilayers is larger compared to (Co/Ni) multilayers. These multilayers could be the basis for spintronic devices where the reduction of total Pt content could help to reduce the damping constant while keeping the magnetic anisotropy energy relatively high. These are conflicting requirements needed for high performance magnetic memory devices. Highlights • New material based on (Co/Ni/Co/Pt) multilayer with perpendicular magnetic anisotropy is investigated. • The magnetic properties were investigated in (Co/Ni/Co/Pt) with different Ni thickness. • Micromagnetic simulation was carried out to reproduce magnetic force microscopy images. • From magnetometry measurements, micromagnetic simulation and temperature dependence of intrinsic properties (saturation magnetization and anisotropy energy), Block constant and spin wave stiffness were determined for each sample.
2012
Ferromagnetic resonance (FMR) spectroscopy, x-ray magnetic circular dichroism (XMCD) spectroscopy and magnetic transmission soft x-ray microscopy (MTXM) experiments have been performed to gain insight into the magnetic anisotropy and domain structure of ultrathin Co9Ni multilayer films with a thin permalloy layer underneath. MTXM images with a spatial resolution better than 25 nm were obtained at the Co L 3 edge down to an equivalent thickness of Co of only 1 nm, which establishes a new lower boundary on the sensitivity limit of MTXM. Domain sizes are shown to be strong functions of the anisotropy and thickness of the film.
Journal of Magnetism and Magnetic Materials, 2012
Ferromagnetic resonance (FMR) spectroscopy, x-ray magnetic circular dichroism (XMCD) spectroscopy and magnetic transmission soft x-ray microscopy (MTXM) experiments have been performed to gain insight into the magnetic anisotropy and domain structure of ultrathin Co9Ni multilayer films with a thin permalloy layer underneath. MTXM images with a spatial resolution better than 25 nm were obtained at the Co L 3 edge down to an equivalent thickness of Co of only 1 nm, which establishes a new lower boundary on the sensitivity limit of MTXM. Domain sizes are shown to be strong functions of the anisotropy and thickness of the film.
Anatomy of large perpendicular magnetic anisotropy in free-standing Co/Ni (1 1 1) multilayer
Journal of Magnetism and Magnetic Materials, 2019
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