Multidomain and single-domain relations between susceptibility and coercive force

Details Multidomain and single-domain relations between susceptibility and coercive force Multidomain and single-domain relations between susceptibility and coercive force

Dec 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987pepi...49..181d&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 49, Issue 3-4, p. 181-191.

Physics

11

Scientific paper

Theoretically, multidomain (MD) initial susceptibility (χ0)init and coercive force Hc are related by 1/(χ0)init = k-1Hc/js + N, in which js is spontaneous magnetization Js normalized to its room-temperature value Js0, N is a demagnetizing factor, and k is a sample-dependent constant of the order of 45 emu cm-3 (4.5 × 104 A m-1) for magnetite. The corresponding single-domain (SD) relation is 1/(χ0)init = k-1Hc/js, with k = 0.319Js0 (for magnetite ~ 150 emu cm-3). The slopes and intercepts of linear plots of 1/(χ0)init and Hc/js data measured at different temperatures should thus reveal domain structure and give a value of N in the MD case. We have tested the equations using data for SD and small MD magnetites, maghemites and titanomaghemites. In most cases the relations were linear, but many of the slopes and intercepts were at variance with theory. Some of the discrepancy between theory and experiment may result from mixtures of SD and MD material and non-uniaxial anisotropies, but most is due to thermal fluctuations. We develop a generalized method of thermal fluctuation analysis (TFA) to deal with such effects in the thermal excitation range below the unblocking temperature.
Now at Institut de Physique du Globe, Université de Paris 7, Place Jussieu, 75252 Paris, France.

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