Figure 3: Curie temperature variation with anneal time.
From: Inferred time- and temperature-dependent cation ordering in natural titanomagnetites
(a) Temperature-dependent susceptibility measurements and (b) derivative curves from samples MSH002-G following annealing at 350 °C for different durations. (c,d) Same data for NV39-A following annealing at 400 °C for different durations. Solid and dashed lines, respectively, indicate measurement on heating and cooling. TC determined from the heating curves increases systematically with anneal time, implying that cation ordering occurs continuously and homogeneously at these temperatures. Cooling curves are virtually identical in all cases, showing that disordered states reached by re-equilibration at T>450 °C are quenched in at the cooling rate of the χ(T) experiment (~10 °C min−1). Note that NV39-A also has a (mostly) reversible TC at ~580 °C associated with oxyexsolved, magnetite-rich grains.
