Physics
Scientific paper
Dec 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982pepi...30..347h&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 30, Issue 4, p. 347-347.
Physics
Scientific paper
Magnetic domain patterns have been observed on particles of natural pyrrhotite and titanomagnetite undergoing hysteresis. These observations indicate that hysteresis properties are governed by two distinct mechanisms: (1) wall-pinning and (2) nucleation of reverse domains. Particles which are dominated by wall-pinning spontaneously nucleate reverse domains in saturation remanence (Jrs). The coercivity of such grains is determined by the presence of potential wells encountered by the wall in its traverse across the grain. However, many pseudosingle-domain particles (PSD) between 5 and 30 μm in diameter do not nucleate reverse domains in Jrs, but remain as saturated single-domains. These particles require a reverse field Hn to nucleate domain walls. When Hn is sufficiently large, the nucleating field controls magnetization reversal by driving the wall across the particle in a single Barkhausen jump, and the muscopic coercivity is nucleation-dominated.
The proportion P (w=0) of particles of a given size d which fail to nucleate walls in Jrs is found to be given by A exp(-Bd1/2), where A and B are experimentally determined constants. The nucleation field Hn in pyrrhotite is observed to increase with decreasing grain size, exceeding 500 Oe in 5 μm particles.
The difficulty with which reverse domains are nucleated subsequent to saturation may thus provide a mechanism for achieving the high values of Jrs/Js and coercive force observed in fine, pseudosingle-domain particles.
Fuller Michael M.
Halgedahl Susan L.
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