Magnetic hysteresis as a function of low temperature for deep-sea basalts containing large titanomagnetite grains-inference of domain state and controls on coercivity

Details Magnetic hysteresis as a function of low temperature for deep-sea basalts containing large titanomagnetite grains-inference of domain state and controls on coercivity Magnetic hysteresis as a function of low temperature for deep-sea basalts containing large titanomagnetite grains-inference of domain state and controls on coercivity

Dec 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982pepi...30..323h&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 30, Issue 4, p. 323-323.

Physics

Scientific paper

Hysteresis loops to 1200 oersteds (9.55×104 A m-1) are measured between 295 K and 105 K for two deep-sea basalts (DSDP, Leg 34 and 37) containing large (~200 μm) unexsolved titanomagnetite grains. The Curie points, electron microprobe analyses and saturation magnetizations of the magnetic grains are the same as for unoxidized synthetic titanomagnetite (xFe2TiO4.(l - x)Fe3O4) with x=0.6.
As temperature is lowered from 295 to 190 K, coercive force Hc slowly rises from ~40 Oe to ~95 Oe approximately in proportion to the rise in the magnetostriction constant λ. Presumably, Hc is controlled by λ through internal stresses impeding domain wall motion. As expected of multidomain grains, the ratio of saturation remanence to saturation magnetization (in 1200 oersted cycles) jR/jS rises approximately in proportion to Hc, with a constant of proportionality consistent with titanomagnetite (x=0.6).
As temperature is lowered from 190 to 120 K, Hc rises rapidly to ~400 Oe as a roughly linear function of the magnetocrystalline anisotropy constant K1. Perhaps Hc is now controlled by K1 through non-magnetic inclusions impeding domain wall motion.
As temperature is lowered from 120 to 105 K, Hc rises even more rapidly to ~600 Oe. The control over Hc seems to have changed again, though most of the titanomagnetite is in grains large enough to still contain a few domains. The ratio jR/jS reaches 0.7 by 105 K and appears to be saturating towards the theoretical limit of 0.83.

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