Domain wall structure in Permalloy films with decreasing thickness at the Bloch to Néel transition

Abstract

Articles you may be interested inPhotoemission electron microscopy study of remanent magnetic domain states in ferromagnetic wedge films deposited on substrates with micrometer-sized square plateaus J. Appl. Phys. 99, 063904 (2006); 10.1063/1.2174119 Variation of domain-wall structures and magnetization ripple spectra in permalloy films with controlled uniaxial anisotropy J. Appl. Phys. 98, 053905 (2005); 10.1063/1.2033152 Magnetic domain wall transitions based on chirality change and vortex position in thin Permalloy™ films Cross-tie walls and magnetic singularities on the surface of permalloy films (abstract)The Bloch to Néel 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 Néel transition takes place between 35 and 30 nm, below which the wall becomes a symmetric Néel 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, 1998͒, p. 251͔ and A. E. Labonte's numerical calculations ͓J. Appl. Phys. 40, 2450 ͑1969͔͒. For the Néel walls, however, our results indicate an approximately 70% higher energy for thicknesses of 30 nm and below, since the Néel 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 Néel 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.

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100)

“…We believe this anomaly can largely be attributed to the nature of the microstructure as the films transition from discrete to coalesced grain structures and a possible accompanying transition in domain dynamics. Trunk and co-authors [37] have shown that a transition from Bloch to Neel domain wall structures takes place with decreasing Py film thickness. Neel wall dynamics were found to govern under conditions where demagnetization effects dominated, and Bloch wall switching begins to emerge as the exchange interaction becomes more prevalent.…”

One-dimensional Néel walls under applied external fields

“…Studies of Néel walls have a long and somewhat controversial history (see the discussions in [2,10]), but at present the structure of the Néel wall in very thin films appears to be rather well understood on the basis of micromagnetic arguments [2,9,[11][12][13][14][15][16][17]. The basic features of the predicted one-dimensional Néel wall profiles had been verified experimentally in [18] (see also [19,20]).…”

Continuous Néel-to-Bloch transition in strips whose thickness increases: Statics and dynamics

“…Despite its fundamental nature, it has been unclear whether the Néel to Bloch transition at h c is continuous or discontinuous. [12,13,14] A recent and comprehensive magnetostatics study by Kakay and Humphrey [15] indicates that the transition between Néel walls and asymmetric Bloch walls is first order, although the authors were cautious in identifying the specific thickness at which the transition occurs.…”