Magnetization reversal nucleation

Traditional magnetization reversal has been discussed in the framework of the nucleation theory. The critical fields which cause an equilibrium magnetic state to change were calculated using stability analysis. In addition to the switching field these theories also revealed the reversal mode [22]. The total energy of a magnetic particle may be written in terms of the... 

For large sizes the particles are multi-domain becoming more bulk-like with increasing size. The mechanism of magnetization reversal is domain wall nucleation and motion for the multi-domain case [1], As the particle size is reduced the increase of energy due to domain wall formation dominates over the decrease in energy attributed to the formation of domains. Thus, below a critical particle size domain walls will no longer... 

Wemsdorfer W, Doudin B, MaiUy D, Hasselbach K, Benoit A, Meier J, Ansermet JP, Barbara B (1996) Nucleation of magnetization reversal in individual nanosized nickel wires. Phys Rev Lett 77 1873-1876... 

The rare earth-cohalt magnets are discussed here with a fairly applied bias. Relevant fundamental subjects are treated exhaustively elsewhere in this handbook series basic magnetic properties of the RE-elements by Legvold (1980), those of RE-TM intermetallics by Buschow (1980), and the theory of hard-magnetic behavior - small-particle magnetization reversal, domain-wall nucleation and motion, and the role of anisotropy in these - by Zijlstra (1982). Buschow (1988) discusses the various mechanisms thought to be controlling the coercivity in all REPM, and the... 

This coercivity is a simple example of a nucleation field. In micromagnetism, the term nucleation refers to the instability of the remanent state in a reverse magnetic field Hz = - //N. It does not necessarily imply localization effects [16, 93], although localized nucleation is frequently encountered in practice. 

Figure 11. Pinning and nucleation. Pinning means that coercivity is created by trapping the domain wall at pronounced inhomogenities (pinning centers). In the absence of pinning centers, the coercivity is determined by the reversal field at which the original magnetization configuration becomes unstable (nucleation).

In this section, we concentrate on the fundamental impact of particle size reduction on magnetization processes in individual particles. Although not directly related to coercivity, the classical effect of single domain particle formation is described. At small particle size, reversal by coherent rotation tends to be favoured with respect to nucleation/pinning-depinning finally thermal activation effects and macroscopic quantum tunnelling are discussed. 

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