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Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Unidirectional Anisotropy In Ultrathin Transition-Metal Films , Ralph Skomski, H.-P. Oepen, J. Kirschner
Unidirectional Anisotropy In Ultrathin Transition-Metal Films , Ralph Skomski, H.-P. Oepen, J. Kirschner
Ralph Skomski Publications
Unidirectional magnetic anisotropies in low-symmetry magnetic thin films such as cobalt on vicinal copper surfaces are investigated. Possible explanations of the observed uniaxial anisotropies are competing anisotropy (CA) coefficients and Dzyaloshinskii-Moriya (DM) interactions. Unidirectional CA is an interesting mechanism occurring in low-symmetry magnets and involves neither antiferromagnetic exchange nor spin canting. It is visible in the easy-cone regime and decides, for example, whether the preferential magnetization direction points up or down a stepped surface. In the case of Co/Cu(11n) films, however, the anisotropy direction speaks in favor of DM-type interactions.
Higher-Order And Next-Nearest-Neighbor Néel Anisotropies , Y.T. Millev, Ralph Skomski, J. Kirschner
Higher-Order And Next-Nearest-Neighbor Néel Anisotropies , Y.T. Millev, Ralph Skomski, J. Kirschner
Ralph Skomski Publications
The problem of higher-order Néel anisotropies is solved by exploiting the addition theorem for spherical functions. A key advantage of the present approach is the orthonormal character of the expansion of the magnetic energy that simplifies the formalism and makes possible the treatment of nonideal morphologies as well. Explicit expressions for second-, fourth-, and sixth-order anisotropies are obtained for ideal bulk of fcc and bcc symmetry as well as for (001), (110), and (111) surfaces with nearest-neighbor (NN) Néel interactions. The systematic examination of the pair model involves partition by species of inequivalent sites, interaction spheres, and orders in the …
Micromagnetics Of Ultrathin Films With Perpendicular Magnetic Anisotropy , Ralph Skomski, H.-P. Oepen, J. Kirschner
Micromagnetics Of Ultrathin Films With Perpendicular Magnetic Anisotropy , Ralph Skomski, H.-P. Oepen, J. Kirschner
Ralph Skomski Publications
Magnetization processes in ultra-thin transition-metal films with perpendicular magnetic anisotropy are investigated. By model calculations it is shown that nucleation in ideal films is incoherent and therefore bulk-like, whereas the truly ultra-thin limit of coherent nucleation is restricted to film patches of small cross-section areas. In ideal mono-layers, the nonzero film thickness leads to bulk-like nucleation if the lateral dimensions of the film exceed about 1 mm. This means that monolayer patches having sub-micrometer diameters cannot be regarded as ultra-thin in a micro-magnetic sense. On the other hand, the critical single-domain diameter of ultra-thin films is larger by one order …
Iron And Nickel Surface And Interface Anisotropies, Ralph Skomski, D. Sander, C. Schmidthals, Axel Enders, J. Kirschner
Iron And Nickel Surface And Interface Anisotropies, Ralph Skomski, D. Sander, C. Schmidthals, Axel Enders, J. Kirschner
Ralph Skomski Publications
The anisotropy of fcc (111) Fe/Ni and Fe/Ni/Fe layers is investigated. The films exhibit an oscillating behavior of the preferential magnetization direction depending on whether the surface layer is Ni or Fe. Anisotropy fields are obtained from polar and perpendicular Kerr hysteresis loops and yield a comparatively small perpendicular Fe/Ni interface anisotropy of about 0.15 mJ/m2. The real-space origin of the interface anisotropy is the interlayer hybridization of the yz, zx, and z2 orbitals.
Magnetoelectric Néel Anisotropies, Ralph Skomski
Magnetoelectric Néel Anisotropies, Ralph Skomski
Ralph Skomski Publications
The applicability of Néel's pair model to metallic 3d surfaces and interfaces is explained in terms of the tight-binding moments theorem. The Néel model reproduces itinerant magnetism so long as the band structure is approximated by third-moment atomic-pair contributions. This establishes an atomic Néel description of interfaces and impurities. The Néel parameter g depends on the d-band filling and, to some extent, on the atomic structure.
Hydrogen In R2Fe17 Intermetallic Compounds: Structural, Thermodynamic, And Magnetic Properties, S. Wirth, Ralph Skomski, J.M.D. Coey
Hydrogen In R2Fe17 Intermetallic Compounds: Structural, Thermodynamic, And Magnetic Properties, S. Wirth, Ralph Skomski, J.M.D. Coey
Ralph Skomski Publications
The absorption and diffusion behavior of hydrogen in iron-rich rare-earth intermetallics of the type R2Fe17 (R=Y, Sm, Gd) and the resulting changes of their magnetic properties are investigated. Intermediate hydrogen concentration indicate the solid-solution character of the hydrides. From equilibrium and nonequilibrium absorption experiments net reaction energies, bulk diffusion constants, and surface barrier energies for Sm2Fe17 are determined and discussed. The low-temperature quantum diffusion is discussed for the hydride and the corresponding nitride. The interstitial modification changes drastically the crystalline electric field in the rare-earth intermetallics. For Sm2Fe17H4 the …
Immobilization Diffusion In R2Fe17 Nitrides, Ralph Skomski, S. Wirth
Immobilization Diffusion In R2Fe17 Nitrides, Ralph Skomski, S. Wirth
Ralph Skomski Publications
The diffusion of nitrogen in R2Fe17 intermetallics is investigated by an approach which reconciles the solid-solution and immobilization theories of nitrogen diffusion. It turns out that two-sublattice diffusions may yield sharp concentration profiles but leave the phase structure of the nitride unchanged. Beside the reaction time and a local relaxation time there exists a global relaxation time which governs the smoothing of concentration gradients. Due to the large number of unknown energy parameters involved it is difficult to make quantitative predictions, but in general the diffusion behavior depends on factors such as the use of N2 …
Finite-Temperature Behavior Of Anisotropic Two-Sublattice Magnets, Ralph Skomski
Finite-Temperature Behavior Of Anisotropic Two-Sublattice Magnets, Ralph Skomski
Ralph Skomski Publications
The finite-temperature magnetism of rare-earth transition-metal intermetallics is investigated by extending the n-component vector spin model to two-sublattice magnets. Mean-field analysis shows that the influence of the rare-earth anisotropy on the mean-field Curie temperature is much smaller than expected from the low-temperature rare-earth anisotropy. The use of ultraspherical polynomials yields a generalization of the famous m (m+1)/2 power-law exponent to m (m+n-2)/( n-1).
Micromagnetic Localization, Ralph Skomski
Micromagnetic Localization, Ralph Skomski
Ralph Skomski Publications
The localization of nucleation modes in inhomogeneous ferromagnets and its influence on the coercivity are investigated. From the formal analogy between quantum mechanics and micromagnetics follows that anisotropy inhomogeneities may cause localization. The nucleation modes of one-dimensional arrays, such as multilayers composed of hard and soft magnetic materials, are localized even if the superlattice exhibits a nearly ideal periodicity. Gaussian distributions of the layer thicknesses lead to Urbach tails and very low coercivities, but a maximum thickness lm of the soft layers suppresses the Urbach tails. The related problem of magnetic viscosity leads to a supersymmetric Fokker–Planck description where …