[en] The remanent state of truncated conical particles is investigated as a function of their size, aspect ratio, and anisotropy, using a micromagnetic model based on the Landau - Lifshitz - Gilbert equation. Particles with a base diameter smaller than three times the exchange length show a 'flower' state, while larger particles show a 'vortex' magnetization state. The critical size for this transition increases with increasing anisotropy. Small flower-state particles show abrupt reorientation from out-of-plane to in-plane magnetization at a critical aspect ratio of 0.9. For vortex-state particles, the axial remanence gradually increases as the aspect ratio increases, and high aspect ratio particles have significant remanence even at larger diameters. [copyright] 2001 American Institute of Physics

[en] The Bloch to Neel wall transition is investigated in Permalloy films between 160 and 10 nm thickness using direct integration of the Landau - Lifshitz - Gilbert equation in a three-dimensional Cartesian lattice. At 80 nm, the wall is a symmetric Bloch wall characterized by two adjoining vortices with the magnetization at the wall center pointing perpendicular to the plane of the material throughout the thickness. The Bloch to Neel transition takes place between 35 and 30 nm, below which the wall becomes a symmetric Ne prime el wall. For the Bloch walls, our wall energy per unit area calculations match reasonably well the results of A. Hubert's Ritz method calculations [Magnetic Domains (Springer, New York, 1998), p. 251] and A. E. Labonte's numerical calculations [J. Appl. Phys. 40, 2450 (1969)]. For the Neel walls, however, our results indicate an approximately 70% higher energy for thicknesses of 30 nm and below, since the Neel wall tails are included. For thicknesses below 160 nm, the anisotropy energy component is low, and both C-shaped and symmetric Bloch walls are dominated by exchange interaction. As the wall transforms from Bloch to Neel below 35 nm, the energy contribution changes from 76% exchange and 24% demagnetization to 70% demagnetization and 30% exchange, respectively. Wall widths are computed for thicknesses between 10 and 640 nm along with the out-of-plane magnetization due to the presence of the vortex. [copyright] 2001 American Institute of Physics

[en] Three-dimensional magnetic structures of pi-vertical-Bloch line (VBL) and 2pi-VBL are investigated in 80 - 320-nm-thick Permalloy films using direct integration of the Landau - Lifshitz - Gilbert equation in an 128x128x80 point Cartesian lattice. A pi-VBL reflects the shapes of its adjacent walls, which change with film thickness. The pi-VBL conducts the flux between walls of opposite chirality by letting the magnetization rotate out of the plane of the walls via a vortex structure. The Neel caps switch chirality via a 'converging point,' or cross-tie, flux at one surface and a vortex flux, or a swirl, at the other surface. The pi-VBL energy per unit area is 0.44, 0.20, and 0.30 erg/cm2 in 80, 160, and 320 nm films, respectively. The corresponding pi-VBL widths are 88, 60, and 86 nm. A stable winding 2pi-VBL structure was also computed by combining two pi-VBL structures of appropriate chirality. The Neel caps intersect via the pair-(swirl, converging point) like flux at both surfaces. The width of the 2pi-VBL is 140 nm and its energy per unit area is 0.57 erg/cm2. [copyright] 2001 American Institute of Physics