Авторы: Liua Q., Yu Y., Muxworthyd A., Roberts A.

2008 г.

Phys.Earth.Planet.Int.

The magnetic properties of magnetite (Fe₃O₄) are strongly dependent on the internal stress related to stress-controlled regions and to closure domains associated with defects. The contribution of internal stress to the low-temperature magnetic properties of magnetite was tested using annealed and unannealed multi-domain (MD) magnetites. During low-temperature cooling, a room temperature-induced saturation isothermal remanent magnetization (SIRM) increased abruptly at the Verwey transition (T_v ∼122 K). In particular, the absolute intensity jump (d_VJ, defined as the jump in SIRM at Tv upon cooling) resulted from the high-coercivity fraction of MD grains.We observe that annealing significantly reduces internal stress and thus decreases the average microcoercivity. Comparison of the alternating field (AF) demagnetization spectra of ıVJ both for annealed and unannealed magnetites directly links ıVJ to the internal stress. It is likely that removal of the closure domain associated with stress-controlled regions was dominant when the peak AF was less than the average micromagnetic coercivity (h_c), resulting in a net increase of d_VJ with increasing AF. However, when the AF exceeded the (h_c) threshold, d_VJ decreased because the stress-controlled regions were demagnetized. Such observations could therefore be useful for estimating the (h_c) of MD magnetite.

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