Surface anisotropy of Ni-Co from ferromagnetic resonance

Quach, Henry; Friedmann, A.; Wu, Chunfang; Yelon, A.

doi:10.1103/physrevb.17.312

Cited by 21 publications

(5 citation statements)

References 7 publications

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“…From the offset in the linear fit, G 0 $ 2 Â 10 8 rad/s is estimated for our multilayer films, which is comparable to those for Ni 28) and Ni 84 Co 16 alloy. 29) Therefore, it is likely that the damping is enhanced mainly at interfaces in contact with Pt layers and does not increase much inside multilayers.…”

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Gilbert Damping in Ni/Co Multilayer Films Exhibiting Large Perpendicular Anisotropy

Mizukami

Zhang

Kubota

et al. 2011

Appl. Phys. Express

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Gilbert damping is reported in perpendicularly magnetized Ni/Co multilayer films with Pt buffer and capping layers, and investigated through the time-resolved magneto-optical Kerr effect under various applied magnetic field strengths and directions. Both damping constant α and perpendicular magnetic anisotropy energy Ku depend strongly on layer thickness and bilayer periodicity, and rise to approximately 0.08 and 8 Merg/cm3, respectively. The Gilbert damping rate depends linearly on inverse multilayer thickness, indicating that large damping in the Ni/Co multilayers stems from its interfaces in contact with the Pt layers.

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confidence: 99%

“…Solid lines are linear fits to the data, and the broken line corresponds to G for bulk-Ni 28) and Ni 84 Co 16 alloy. 29)…”

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confidence: 99%

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Gilbert Damping in Ni/Co Multilayer Films Exhibiting Large Perpendicular Anisotropy

Mizukami

Zhang

Kubota

et al. 2011

Appl. Phys. Express

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“…However, it is not a conclusive evidence because the magnitude of the surface anisotropy was not measured directly, but chosen to fit the theoretical to the experimental size-dependence. The value used in [21] is similar to surface anisotropies measured [23] in similar materials, but such fitting always leaves some doubt. It is thus not quite clear if the effect of the surface anisotropy is the true and the whole story, or if there is an alternative or supplementary reason for the observed size-dependence of the resonance frequencies.…”

Section: Exchange Resonance Modesmentioning

confidence: 63%

The Special Role of Magnetization Curling in Nanoparticles

Aharoni

2002

phys. stat. sol. (a)

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A qualitative change can occur, in a certain particle size, if the magnetization reverses by the curling mode, as demonstrated by superparamagnetic spheres, and by the initial susceptibility of ideally-soft spheres and disks. The theory of exchange resonance modes in small ferromagnetic spheres is extended to the case of a sphere whose centre is not ferromagnetic, as is the case when the magnetic particle is grown around a non-magnetic nucleus, such as the fine particles of the alloys of Fe, Co, and Ni that are made around a nucleus of a noble metal. A first-order calculation leads to a negligible modification of the eigenvalues for the inner radius used in the experiments. For larger holes, the change can be measurably large for some modes. IntroductionThe theory of micromagnetics has never been able [1] to account for the magnetization processes in bulk ferromagnets. It is commonly believed that these processes are mostly governed by crystalline imperfections in hard materials, and by surface roughness and internal voids in soft materials. Both types help the nucleation of reversed domains on the one hand, and hinder the motion of the walls on the other hand. In both cases, however, the mechanisms are not sufficiently clear, and there is no satisfactory theory for them. There are many numerical simulations, but the results always look as if something is still missing there [2], so that they do not even seem promising yet, and it is not really known how to proceed.The situation is much better with fine ferromagnetic particles, for which it is energetically unfavorable to subdivide into domains, thus eliminating the most difficult theoretical problem of nucleation and growth of reversed domains. Theoretical nucleation fields are [3] close to the experimental coercivities of nearly-perfect whiskers for small whisker radius, but are off by several orders of magnitude for larger radii, thus indicating that the effect of body and surface imperfections is less important in fine particles than it is in larger ones. The computer resources necessary for numerical study of particles, by subdividing them into a sufficiently fine mesh, is also manageable when the particles are not too large. Moreover, there are now several experimental studies of individual particles, with which it should be easy to compare the theoretical results, without the problem of interactions between particles that complicated the analysis of older experiments. And there are some analytic results for ideal particles that can be used as a start and a guidance for the study of less perfect particles.It should thus seem natural for numerical micromagnetics to concentrate on extending the analytic results, by studying the effects of imperfections, and of other phenomena neglected in the old theory, such as surface anisotropy, magnetostriction, etc. For some historical reasons, however, numerical computations have been [2] mostly search-

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“…Also, the surface has been observed [6,7] to contain impurities, mainly C and O. The particular form assumed for a surface anisotropy could [5] fully account for the experimental dependence on the particle size, with a fitted magnitude of the order of surface anisotropies measured [8,9] in similar materials. The same form of surface anisotropy was also found later [10] to account for the resonance data in MnFe 2 O 4 nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

Exchange Resonance Modes in a Hollow Sphere

Aharoni

2002

phys. stat. sol. (b)

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The theory of the exchange resonance modes is extended to the case of a sphere with a nonmagnetic core, such as the fine particles of ferromagnetic alloys that are grown around a nucleus of noble metals. A first-order calculation leads to modified eigenvalues as a function of the radius of the inner sphere, which turns out to be hardly noticeable for the inner radius used in the published experiments. For larger holes, this modification is negligibly small for some modes, but can be measurably large for other modes.

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Surface anisotropy of Ni-Co from ferromagnetic resonance

Cited by 21 publications

References 7 publications

Gilbert Damping in Ni/Co Multilayer Films Exhibiting Large Perpendicular Anisotropy

Gilbert Damping in Ni/Co Multilayer Films Exhibiting Large Perpendicular Anisotropy

The Special Role of Magnetization Curling in Nanoparticles

Exchange Resonance Modes in a Hollow Sphere

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