Structure of macrodomain walls in polytwinned magnets

Abstract

We propose a microscopic approach to the studies of magnetic configurations in hard magnets which may be conveniently used for nanoscale systems; the microstructure of the magnet is easily and naturally included in the calculations. This approach is applied to find the structure of macrodomain walls in polytwinned magnets of the CoPt family. Magnetostatic fields are small compared to the anisotropy field in these magnets; direct simulation shows that in this case the macrodomain wall is not continuous, but rather comprised of segments held together by relatively small magnetostatic forces. This segmentation is expected to have a strong effect on magnetization processes.

Finite-temperature anisotropy of PtCo magnets

“…The calculation of the free energy (5) is straightforward and yields the anisotropy (6) In this equation, enters the zero-temperature anisotropy , where , but not the temperature-dependent term. The temperature dependence of originates from in (4).…”

“…T ETRAGONAL intermetallics having in the structure, such as PtCo, PdFe, and PtFe, have attracted much attention as permanent magnets and, more recently, in the field of magnetic recording [1]- [6]. One reason is the comparatively large magnetocrystalline anisotropy, about 4.9 MJ/m for PtCo.…”

Atomic and micromagnetic aspects of L10 magnetism

“…Scientifi c interest has been fueled by the specifi c features of L1 0 magnets, such as the layered crystal structure, the two-sublattice nature of the magnetism, and the simultaneous involvement of 3d and 4d/5d electrons, and continuum [9] and atomistic models [11], micromagnetic simulations [12], fi rst-principles calculations [13] and [14], and multiscale approaches [15] are now being used or developed to describe the new nanoscale materials.…”

Anisotropy of exchange stiffness and its effect on the properties of magnets

“…For A c = A ab the domain wall segments slant so as to decrease the surface tension. Segments of a (110) macrodomain wall carry magnetic charges of alternating signs, 43 and the flux closure length l f is obviously of the order of the c-domain thickness d. Therefore, at d > ∼ l cr the magnetostatic interaction dominates, and the segments align parallel to the tetragonal axis to get rid of the magnetic charge, while at d ≪ l cr their orientation is determined by Eq. (13).…”

“…These walls are split at the twin boundaries, and their segments are coupled only by relatively weak magnetostatic forces. 43 Below we study the effects of exchange stiffness anisotropy on the properties of macrodomain walls. We will describe the orientation of macrodomain wall segments, the energetical preference of different global macrodomain wall orientations, the rotation of segments during macrodomain wall splitting in external field, and the relation of these properties with coercivity.…”