Temperature dependence of hysteresis in 0.04-0.22 μm magnetites and implications for domain structure

Details Temperature dependence of hysteresis in 0.04-0.22 μm magnetites and implications for domain structure Temperature dependence of hysteresis in 0.04-0.22 μm magnetites and implications for domain structure

Jun 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987pepi...46..100d&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 46, Issue 1-3, p. 100-119.

Physics

25

Scientific paper

Initial susceptibility χ0, second Rayleigh coefficient B0, coercive force Hc, remanent coercive force HR, and near-saturation remanent and induced magnetizations Jrs and Js have been measured at a series of temperatures between ambient and 575° C for dispersed submicron magnetites with mean crystal sizes of 0.037, 0.076, 0.10 and 0.22 μm.χ0 and B0 reach a Hopkinson peak just below the Curie point, and χ0(T) data are well explained by reversible domain-wall displacements. Saturation remanence has three distinctive characteristics: (1) its dependence on particle size d changes smoothly from d-0.75 at room temperature to d-0.6 at 500° C; (2) Jrs(T) varies as Hc(T) up to 300° C and as HK(T) at higher temperatures (HK is microscopic coercive force corrected for thermal fluctuations); (3) Jrs/Js decreases steadily as the temperature rises. Neither failure of domain-wall nucleation following saturation nor domain-wall moments can reconcile these observations, but they are explained in a natural way by domain wall displacements, particularly if the average number of domain walls per particle increases at high temperature. Other experimental evidence indicates that the equilibrium single-domain to two-domain transition size remains essentially constant up to 500° C. However, apparent demagnetizing factors N = HK/Jrs suggest a decrease in the 2-domain to 3-domain and 3-domain to 4-domain transition sizes at high temperatures.

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